Reagents for rapid peptide synthesis

ABSTRACT

The compounds of the present invention are adaptable as blocking or protecting groups for an amine composition useful in peptide synthesis. The present invention is directed to a method of protecting an amino group of an organic molecule during a reaction which modifies a portion of the molecule other than the protected amino group.

This invention was made with Governmental support under RO1-GM-9076awarded by the National Institute of Health. The Government has certainrights in the invention.

This is a continuation of application Ser. No 08/038,414 filed on Mar.29, 1993, now U.S. Pat. No. 5,510,491, which is a divisional of U.S.Ser. No. 944/806 filed Sep. 14, 1992 now U.S. Pat. No. 5,221,754 whichis a continuation of U.S. Ser. No. 774,386 filed Oct. 11, 1991 nowabandoned which is a continuation of U.S. Ser. No. 364,662 filed Jun. 9,1989 now abandoned.

FIELD OF THE INVENTION

This invention relates to 2-propenyl chloroformate compounds andderivatives thereof and their use in synthetic biochemistry, includingpeptide synthesis. More particularly, this invention relates to the useof these compounds as blocking groups which attach to primary andsecondary amino groups to protect the amino group from undergoingundesirable side reactions during peptide synthesis.

BACKGROUND OF THE INVENTION

Support for the research leading to this invention was sponsored, inpart, by the National Institute of Health. This support is gratefullyacknowledged by the inventors.

A basic problem in peptide synthesis is one of blocking or protectingthe amino group from interaction with a carboxyl group on the same aminoacid. These undesirable side reactions are prevented by attaching to oneamino acid a group that will render the --NH₂ group unreactive and stillpermit the desired reaction to take place. In addition to providingprotection for the amino group, the blocking group is preferably onethat can be easily removed without chemically altering the remainder ofthe molecule including the peptide linkage that has been built up duringthe synthesis. (See generally, Morrison and Boyd, Organic Chemistry,Third Ed., Sec. 30.10 Synthesis of Peptides, pp. 1131-1133 (1983).

Attempts to develop a two-support continuous solid phase technique forpeptide synthesis (inverse Merrifield method) using a9-Fluorenylmethyloxycarbonyl group (FMOC) for amino protection have beenhindered due to incomplete scavenging of dibenzofulvene by the polymericdeblocking agents. These problems were partially overcome through use ofthe the 2-Chloro-1-indenylmethoxycarbonyl group (Climoc) for protectionof amino groups (see U.S. Pat. Nos. 4,581,167 and 4,394,519 to Carpino,et al.). The present invention has devised a scheme for the developmentof new, Michael-addition based amino-protecting groups for which thedeblocking and scavenging steps are one and the same.

The present invention is directed to compounds containing novel Michaeladdition based amino-protecting groups, such as2-(t-butyl-sulfonyl)-2-propenyloxycarbonyl groups and the like. The useof the compounds of the present invention in peptide synthesis overcomesthe problems resulting from ineffective scavenging occurring when theFMOC or Climoc groups are utilized as the protecting groups.

The 2-(t-Butylsulfonyl)-2-propenyloxycarbonyl group (Bspoc) and relatedMichael Addition-based amino-protecting groups described herein aresuperior for peptide synthesis. Deblocking is exceptionally rapid undermild, nonhydrolytic conditions, resulting in faster syntheses of longchain peptides with fewer side reactions, such as diketopiperazine,pyroglutamic acid and succinimide formation, thereby leading to higheryields and greater purity of the products. Due to the stability againstacidic reagents, acid chlorides may be used as quick-acting couplingagents, further speeding up the process. Moreover, no significantracemization occurs in either the coupling or deblocking steps.

SUMMARY OF THE INVENTION

This invention relates to compounds for use as blocking groups toprotect a primary or secondary amino group from side reactions. Thesecompounds will be stable under acidic reaction conditions, preventingside reactions at the amino site. When protection of the amine is nolonger required, these groups are rapidly removed by treatment with anucleophile.

The compounds of this invention react readily with primary or secondaryamines to form carbamates as described hereinbelow. Formation of thesecarbamates protects the amino group from further reaction underconditions which modify another portion of the molecule, e.g., formationof a peptide bond whereby said amino protected amino acid reacts with anunprotected amino portion of another amino acid.

Important compounds of the invention are 2-propenyloxycarbonyl compoundshaving the general formula 1: ##STR1## wherein R is an electronwithdrawing group, R₁ is H or COZ, X₁ and X₂ are independently H, loweralkyl, aryl, aryl lower-alkyl or a solid support or R and X₁ takentogether with the carbon atoms to which they are attached form a ringcontaining from 4 to 15 ring carbon atoms and may contain up to 2heteroatoms, wherein the heteroatoms are O, S or N; and Z is a leavinggroup, an amino acid residue or a peptide residue.

These compounds can be derived from alcohols of the formula 2: ##STR2##wherein R, X₁, and X₂ are as hereinbefore defined.

As embodied and broadly described herein, the invention also comprises amethod for protecting a primary or secondary amino group of an organicmolecule during a reaction which modifies a portion of the moleculeother than the protected amino group.

The method comprises the steps of (a) bonding the 2-propenyloxycarbonylcompound of formula I with an amine, thereby protecting said amine fromfurther reaction; (b) modifying a portion of the organic molecule otherthan the protected amine, by chemical reaction; and, (c) cleaving theprotecting group from the amino group.

In a preferred embodiment, the protecting group can be rapidly andcleanly deblocked via treatment with a nucleophile. The nucleophile canalso act as a scavenger for the protecting group. The preferrednucleophile is a primary or secondary amine.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Reference will now be made in detail to present preferred embodiments ofthe invention, examples of which are illustrated hereinbelow.

The present invention is directed to compounds of the formula 1:##STR3## wherein R is an electron withdrawing group;

R₁ is H or COZ;

X₁ and X₂ are independently H, lower alkyl, aryl, aryl lower-alkyl or asolid support or R and X₁ taken together with the carbon atoms to whichthey are attached form a ring containing from 4 to 15 ring carbon atomsand may contain up to 2 heteroatoms wherein the heteroatoms are O, S orN; and

Z is an amino acid residue, a peptide residue or a leaving group.

An electron withdrawing group as defined herein shall be interpreted asa group that will draw electrons to itself more than a hydrogen atomwould if it occupied the same position in the molecule. See, J. March,Advanced Organic Chemistry, 3rd Ed., John Wiley & Sons, P.17 (1985).These types of groups are well-known to one skilled in the art.

Examples of electron withdrawing groups include SO₂ R₂, SOR₂, COOR₂,COR₂, CHO, CONR₂ R₃, CN, CF₃, NO₂, aryl, pyridyl and the like, whereinR₂ and R₃ are independently lower-alkyl having from 1 to 6 carbon atoms,aryl, aryl lower-alkyl, hetero-aryl or a solid support and the alkyl,aryl or hetero-aryl groups are unsubstituted, or mono- or di-substitutedwith halides, SO₂ R₂, SOR₂, COOR₂, COR₂, CHO, CN, CF₃ or NO₂.

As used herein, the terms lower alkyl, when used singly or incombination, refer to alkyl groups containing one to six carbon atoms.They may be straight chain or branched and include such groups asmethyl, ethyl, propyl, isopropyl, butyl, sec-butyl, isobutyl, t-butyl,pentyl, isopentyl, neopentyl, hexyl and the like. The preferred alkylgroups contain one to four carbon atoms.

The term aryl, when used alone or in combination, refer to an aromaticring containing six to ten ring carbon atoms. The aryl group includesphenyl, and 1 or 2-naphthyl. The preferred aryl group is phenyl.

The most preferred aralkyl group is benzyl.

The term hetero-aryl when used alone or in combination refers to anhetero-aromatic ring having from four to nine carbon ring atoms and oneor two hetero ring atoms. The heterocyclic rings may contain sulfur,nitrogen or oxygen. The hetero-aryl groups include quinolyl,isoquinolyl, furyl, thienyl, or pyridyl.

The preferred heteroaryl groups are 2- or 4-pyridyl.

The preferred R groups are SO₂ R₂, SOR₂, COOR₂, COR₂, CONR₂ R₃, aryl, orpyridyl, wherein R₂ and R₃ are as defined hereinabove.

Especially preferred R groups are SO₂ C(CH₃)₃, SOC(CH₃)₃, SO₂ C₆ H₅,SOC₆ H₅, 2-pyridyl, or 4-pyridyl or COOEt.

As used herein the term solid support when used singly or in combinationrefers to polymer resins typically used in peptide synthesis. Thesepolymers are generally employed in the form of beads. The polymer resinspreferred for peptide synthesis are polystyrenes, polyacrylamides andthe like. The preferred polystyrene resin is a copolymer ofstyrene-divinylbenzene.

As noted hereinabove, R and X₁ taken together with the carbons to whichthey are attached may be cyclic containing one, two, or three rings.Said cyclic structure may contain from four to fifteen ring carbon atomsand up to two heteroatoms. These heterocyclic ring atoms may be sulfur,oxygen or nitrogen. For example, when R and X₁ taken together form aring, the compound of the present invention may have the formula 3 orits isomer 3a: ##STR4## wherein B is a chemical bond, CR₈ R₉, ##STR5##SO₂, SO, RP(O), or S, R is lower alkyl or OR₁₀, R₁₀ is lower alkyl, R₈,R₉, R₁₂ and R₁₃ are independently hydrogen or lower alkyl, G is a monoor bicyclic fused ring system containing 5 to 10 carbon atoms and maycontain up to 2 heteroatoms, F is a chemical bond, CR₁₂ R₁₃, S₂, SO,RP(O) or S, R₁₁ is hydrogen or lower alkyl and X₂ and R₁ are as definedhereinabove. G may be completely saturated, partially unsaturated orfully aromatic (e.g. a benzo system). Examples of G include cyclopentyl,cyclohexyl, cyclopentenyl, cyclohexenyl, decalinyl, phenyl, naphthyl,pyridyl azaindenyl and the like.

As defined hereinabove, when F is a chemical bond, then 3 or 3a has thestructure ##STR6##

Similarly, when B is a chemical bond, then 3 or 3a has the structure##STR7##

However, in order to be effective, either B or F is an electronwithdrawing group or ring G is itself electron withdrawing. In otherwords, if ring G is heterocyclic, i.e., contains ring heteroatoms, thenB and F are independently any of the values described hereinabove.However, if ring G is not heterocyclic (e.g. is aromatic or cycloalkyl),then at least one of B or F is ##STR8## SO₂, SO, RP(O) or S wherein R isas defined hereinabove.

A preferred class of 3 or 3a has the formula ##STR9## wherein B is CR₈R₉ or SO₂ and E and D are independently CH or N, provided that when B isCR₈ R₉, then E or D is N.

A preferred embodiment has the formula 4: ##STR10## or the formula 4a or4b: ##STR11## wherein X₂ and R₁ are as defined hereinabove and R₈ and R₉are independent.

When compounds of the present invention are used to protect a primary orsecondary amino group and introduce the 2-propenyloxy carbamate compoundof Formula I, Z is a leaving group. As is generally known in the art andfor the purposes of the present invention "a leaving group" is definedas a group which is readily broken away from its union with the carbonatoms. It is one which readily joins, for example, with an activehydrogen atom to split out a compound containing the hydrogen atom andthe leaving group. Leaving groups are generally electron attractinggroups either because of their electronegativity or because they have aninductive effect. Leaving groups are defined in U.S. Pat. No. 4,394,519to Carpino, et al. which is incorporated herein by reference.

The preferred leaving groups Z are halo, CN, SR₄, SAr, N₃, OAr,##STR12## wherein R₄ is lower-alkyl, aryl or aryl lower-alkyl, whereinthe alkyl or aryl groups are unsubstituted, or mono- or di- substitutedwith halides, SO₂ R₄, SOR₄, COOR₄, COR₄, CHO, CN, CF₃ or NO₂.

The most preferred leaving groups are halo, especially Cl and Br.

When Z is an amino acid residue or a peptide residue it becomes part ofa stable system. An amino acid residue as defined herein as an aminoacid or derivative thereof, such as an ester and the like, minus anamine hydrogen on the amino end of the molecule. A peptide residue is apeptide of two or more amino acids or derivatives thereof, such as anester and the like, linked through an amide bond and it contains oneless amino hydrogen on the amino end of the peptide.

In a preferred embodiment Z is an alpha-amino acid.

The alpha-amino acids are those which are well known to one skilled inthe art. These amino acids, e.g., the naturally occurring alpha-aminoacids, are often used in the chemical synthesis of peptides. These aminoacids include alanine, arginine, asparagine, aspartic acid, cysteine,cystine, glutamic acid, glutamine, glycine, histidine, hydroxylysine,hydroxyproline, isoleucine, leucine, lysine, methionine, phenylalanine,proline, serine, threonine, tryptophan, tyrosine, valine, penicillamine,and the like.

The preferred groups in the vinyl position, X₁ and X₂, are independentlyH, phenyl, lower alkyl having from 1 to 4 carbon atoms or a solidsupport. Especially preferred groups for X₁ and X₂ are independently Hor phenyl. The X₁, and X₂ positions may also be used as the site ofattachment to a polymer resin, On Z, when, Z is an amino acid or peptideresidue.

The preferred compounds of the invention have the formula 1: ##STR13##wherein R is SO₂ R₂, SOR₂, COOR₂, CONR₂ R₃, aryl or 2- or 4-pyridyl,wherein R₂ and R₃ are as defined hereinabove or R and X₁ taken togetherwith the carbon atoms to which they are attached form a ring, the ringhaving from 4 to 15 ring carbon atoms and up to a total of 3 rings,often forming a fused benzo-system; R₁ is H or COZ and Z is halo or anamino acid; and X₁ and X₂ are independently H, phenyl or lower alkyl.

The preferred groups in compounds wherein R and X₁ are taken togetherwith the carbon atoms to which they are attached are SO₂ C₆ H₄ or C₅ H₃NCH₂ thereby describing compounds of the formula 4 or 4a or 4b describedhereinabove: ##STR14## wherein R₁ and X₂, R₈ and R₉ are as definedhereinabove, and R₈ and R₉ are independently hydrogen or lower alkyl.

The most preferred compounds of the invention are the 2-propenyloxychloroformates wherein R is SO₂ C(CH₃)₃, SOC(CH₃)₃, SO₂ C₆ H₆, SOC₆ H₆,COOEt, 2-pyridyl or 4-pyridyl; Z is Cl or Br; and X₁ and X₂ are H orphenyl.

The preferred alcohols of the present invention are:

2-(t-butylsulfonyl)-2-propenyl alcohol,

2-carboethoxy-2-propenyl alcohol,

2-(phenylsulfonyl)-2-propenyl alcohol,

(E)-3-phenyl-2-(phenylsulfonyl)-2-propenyl alcohol,

(Z)-3-phenyl-2-(phenylsulfonyl)-2-propenyl alcohol,

3,3-diphenyl-2-(phenylsulfonyl)-2-propenyl alcohol,

Benzothiophenesulfone-2-methanol,

3,3-dimethyl-2-(phenylsulfonyl)-2-propenyl alcohol.

The preferred chloroformates of the present invention are:

2-(t-butylsulfonyl)-2-propenyl chloroformate,

2-carboethoxy-2-propenyl chloroformate, 2-(phenylsulfonyl)-2-propenylchloroformate,

(E)-3-phenyl-2-(phenylsulfonyl)-2-propenyl chloroformate,

(Z)-3-phenyl-2-(phenylsulfonyl)-2-propenyl chloroformate, or

3,3-diphenyl-2-(phenylsulfonyl)-2-propenyl chloroformate,

Benzothiophenesulfone-2-methyl chloroformate,

3,3-dimethyl-2-(phenylsulfonyl)-2-propenyl chloroformate.

The 2-propenyloxy carbonyl compounds outlined hereinabove can be formedby art-recognized techniques known to one skilled in the art. Exemplaryprocedures are outlined hereinbelow.

The compounds of the present invention having the formula 1a: ##STR15##can be prepared from the corresponding alcohol 2: ##STR16## asillustrated in the following equations: ##STR17## wherein Z=Y=Cl, Br,Fl, CN;

Z=Cl , Y=SR₄, SAr, OAr, F/; ##STR18## wherein Z=C₁, Br; Y=Fl, N₃, CN.

In the above equations, X₁, X₂, R, and R₄ are as defined herein.

Typically, reactions such as indicated by Equation (1) are carried outin an inert organic solvent. As defined herein an inert solvent is areaction inert solvent, i.e., one which will not react with the reagentsor reactants under the given reaction conditions. Suitable solvents arehalogenated or non-halogenated hydrocarbons containing up to about eightcarbon atoms, e.g., methylene chloride, ethylene dichloride, benzene,isooctane and the like. Reactions are conducted at temperatures of fromabout 0° C. to about 25° C. during a reaction period of from about 1 toabout 6 hours. Suitable yields are obtained with equimolar quantities ofreactants, although the yield may often be appreciably increased byutilizing an excess of either one of them, for example, up to about a20% molar excess. Generally speaking, the halogen substituted compoundsare prepared under less rigorous reaction conditions than are requiredfor the preparation of those compounds wherein the substituent is ofhigher molecular weight. The presence of a weak base, may increase therate of reaction.

Reactions of Equation (2) in which the substituent placed on thecarbonyl carbon atom is initially present in an ionic form are carriedout in inert polar organic solvents which will enhance ionization,including, for example, acetonitrile, dimethylformamide,dimethylsulfoxide, tetrahydrofuran, dioxane and the like. The reactionis normally carried out at a temperature of from about 0° C. to about25° C. during a period of from about 1 to 5 hours. Preferably equimolarquantities of reactants are employed to minimize side reactions but amoderate excess of either reactant would not introduce appreciabledifficulties.

Compounds of Formula 2 can be prepared by reacting an aldehyde or ketoneof Formula 5: ##STR19## a Wittig reagent, .O slashed.₃ PCHR, ##STR20##or (R₁₁)₃ S_(i) CH₂ --R such as, ##STR21## where R is definedhereinabove, and R₁₁ is lower alkyl under Wittig reaction conditions;followed by the addition of formaldehyde under Prins reactionconditions, wherein X₁, X₂ and R are as hereinbefore described and R₁₁is lower alkyl.

The compounds of the present invention wherein R contains a sulfur atomcan be prepared by an alternative route. The following procedures asdepicted in Scheme I is illustrative for the preparation of thesecompounds: ##STR22##

An allylic halide such as allyl bromide (6), is treated with a thiol, R₂SH, such as t-butylthiol in strong base to form the correspondingthioether 7. Halogenation of the thioether forms the dihalo thioether 8which in turn is oxidized with an oxidizing agent to form the sulfonylor sulfinyl compound 9. Various oxidizing agents can be used to effectsaid reaction, such as MCPBA. Compound 9 is then reacted with a strongbase, such as lutidine, to form the corresponding unsaturated compound10. Substitution of the halide in compound 10 with hydroxide forms thecompound of Formula 2. The compound of Formula 1 can be readily preparedfrom 2 according to the procedure described hereinabove.

Typically, the reactions for synthesis of the compounds described inScheme 1 hereinabove are carried out in an inert organic solvent.Suitable solvents include alcohols, such as methanol, ethanol,isopropanol, t-butanol and the like, ethers such as diethyl ether,1,4-dioxane, tetrahydrofuran (THF) and the like, hydrocarbons, such asbenzene, hexane, cyclohexane, toluene, Skelly solvents and the like, andhalogenated hydrocarbons such as CHCl₃, CCl₄, CH₂ Cl₂ and the like.

Temperatures for these reactions range from about -78° C. to the refluxtemperature of the solvent being employed. Unless indicated to thecontrary in the discussion of the various reaction schemes describedhereinabve and hereinafter, the preferred temperatures are from about 0°C. to about 100° C.

The compounds described hereinabove can be used to protect primary andsecondary amines. In fact, an embodiment of the present invention isdirected to the method for protecting a primary or secondary amino groupon an organic molecule during a reaction which modifies a portion of themolecule other than the protected amino group, comprising the steps of:

a) reacting the amine with a compound of the formula: ##STR23## whereinZ is a leaving group;

X₁ and X₂ are independently H, lower alkyl, aryl, aryl lower-alkyl or asolid support;

R is an electron withdrawing group; or

R and X₁ with the carbon atoms to which they are attached form a ringcontaining from 4 to 15 ring carbon atoms and up to two heteroatomsselected from the group consisting of nitrogen, sulfur or oxygen;

b) modifying a portion of the molecule other than the protected amine,by chemical reaction; and

c) removing the protecting group from the amino group.

The reagents described hereinabove are useful in protecting primary orsecondary amino groups during synthesis of organic molecules includingbioorganic molecules, e.g., peptides and polypeptides, nucleotides andpolynucleotides.

An application of the present invention is using the compounds describedherein wherein Z is a leaving group to protect the amino group in anamino acid during peptide synthesis. Therefore, the present invention isalso directed to the method for the preparation of a peptide whichcomprises:

a) reacting an amino acid having a free amino group with a compound ofthe formula: ##STR24## wherein Z is a leaving group;

X₁ and X₂ are independently H, lower alkyl, aryl, aryl lower-alkyl or asolid support;

R is an electron withdrawing group; or

R and X₁ with the carbon atoms to which they are attached form a ringcontaining from 4 to 15 ring carbon atoms;

b) reacting the product of (a) with an amino acid or peptide having afree amino group; and

c) removing the protecting group.

Thus in the most preferred embodiment, compounds of the presentinvention can be used as blocking groups for amino acids during peptidesynthesis. The preferred amino acids are alpha-amino acids.

More specifically, the compounds of Formula 1a, wherein Z is a leavinggroup, can react with a carboxyprotected amino acid as indicatedhereinbelow in Scheme II: ##STR25## In the above scheme, X₁, X₂, R, Zare as defined above, and R₇ NH₂ (11) is an alkyl or aryl amine or analpha-amino acid. Examples of the amines are aniline, p-chloroanilineand the like. The alpha-amino acids are the alpha-amino acids describedherein above and include phenylalanine, glycine, valine, and the like.Often the amino acids are protected by a carboxy protecting group knownin the art.

A variety of carboxy protecting groups known in the art may be employed.Examples of many of these possible groups may be found in "ProtectiveGroups in Organic Synthesis" by T. W. Green, John Wiley and Sons, 1981.The preferred carboxy protecting group is the t-butyl ester.

In the above scheme, a compound of Formula 1a is reacted with a carboxyprotected amino acid to form 12 which is then hydrolyzed in acid to forma compound of Formula 1 wherein Z is an amino acid adduct. The mostpreferred protecting group are Bspoc; i.e.,2-(t-butylsulfonyl)-2-propenyloxycarbonyl and Bsmoc, i.e.,Benzothiophenesulfone-2-methyloxycarbonyl.

If the leaving group is a halogen, especially chlorine, the reaction maybe effected in an inert, polar organic solvent such as dioxane,tetrahydrofuran, dimethylformamide, pyridine or other solventcontaining, for example, up to eight carbon atoms. The reaction is rununder alkaline conditions, typically dilute aqueous alkali metal basesuch as sodium or potassium hydroxide or carbonate, at low temperatures,for example, from about 0° C. to 25° C. during a period of from about 2to 3 hours. Usually the protected amino acid or peptide will precipitateupon acidification of the mixture, and may be purified by anyappropriate method such as recrystallization. Excess blocking reagentmay be employed, even up to 0.5 molar excess, but equimolar quantitiesof reactants generally give better results.

The protected amines can also be prepared by reaction of the 2-propenylalcohols with isocyanates. This reaction will form a 2-propenylcarbamate directly without requiring the conversion of the alcohols tochloroformate.

PREPARATION OF PEPTIDES

The 2-propenyloxy carbonyl group, once placed on the amino function tobe protected is especially stable. This makes it possible to use avariety of methods for forming peptides without danger of cleavage ofthe protecting group. In fact, the group is stable under acidicconditions, such as using hydrogen bromide or chloride in variousorganic solvents, or trifluoroacetic acid, involved in the removal ofmost of the commonly used protecting groups. This is a special advantageof the particular compounds of this invention; their use greatlyincreases the options available to the skilled peptide chemist for thepreparation of complex polypeptides.

For coupling an N-protected amino acid or peptide of this invention witha free amino group of another amino acid or peptide to produce di-,tri-, and higher oligopeptides, any of a wide variety of procedures areavailable. Generally speaking, most of the coupling procedures normallyemployed by the skilled practitioner can be used. For example, a carboxyprotected amino acid can be reacted with an amino-protected amino acidunder peptide forming conditions, i.e., amide forming conditions, in thepresence of a coupling agent, such as dicyclohexylcarbodiimide (DCC). Inthis way, amino acids can be added to the chain sequentially until thedesired peptide is synthesized.

The use of activated esters, suitable aryloxy or thioaryl esters,especially substituted phenyl esters such as p-nitrophenyl orpentafluorophenyl esters, also leads to satisfactory results. In fact,most of the procedures used for the placement of the2-propenyloxycarbonyl function for the protection of an amino group canbe used for the coupling reaction.

One coupling procedure which is especially favored is to convert thefree carboxy end of the 2-propenyloxycarbonyl protected amino acid orpeptide into an N-hydroxy succimimide or 1-hydroxybenzotriazole (HOBt)ester. This may be accomplished using dicyclohexylcarbodiimide. Theester is coupled with the amino group under alkaline conditions in aninert, polar, organic solvent such as dimethylformamide, an ester, etheror alcohol containing up to about six carbon atoms. Any mild alkalinereagent such as alkali metal hydroxides, carbonates or bicarbonates, oralkali metal salts of lower aliphatic carboxylic acids can be employed.If the amino acid or peptide to be coupled is in the form of an ester,sodium acetate in water is the preferred alkaline reagent. If it is inthe form of a free acid, sodium hydroxide is the preferred reagent. Thereaction takes place at from about 15° C. to about 30° C. during aperiod of from about 10 to 50 hours. It is generally most economical touse a slight molar excess, e.g., up to about 20% molar excess of one ofthe reactants, although equimolar quantities can also be employed.

It will be apparent, also, that in the course of the synthesis, it maybe necessary to protect certain groups to prevent unwanted sidereactions. For example, it may be necessary to protect the hydroxylgroup of tyrosine, a delta or gamma carboxyl group of aspartic orglutamic acid, or the epsilon amino group of lysine so as to preventinterference by these groups in the main desired reaction. This is acommon problem in peptide synthesis and many procedures are availablefor dealing with it. Such procedures are known to the skilled peptidechemist. (See for example, "Reagents for Organic Synthesis", by T. W.Green, John Wiley and Sons 1981.)

Any of the usual groups employed for protecting or blocking carboxylgroups in peptide chemistry can be employed in this instance. Theprincipal criteria for selection of such groups, as is well known to theskilled artisan is that they should be easily placed on, stable to thereaction condition, and easily removed. Generally, the most preferredprocedure is to form esters according to procedures known to one skilledin the art, and this is the preferred procedure for this reaction. Thepreferred esters are alkyl or alkaryl groups containing up to eightcarbon atoms such as methyl, ethyl, tert-butyl, phenyl, benzyl, orp-methylbenzyl.

CLEAVAGE OF THE PROTECTING GROUP

As mentioned above, a special advantage of the particular novelcompounds of this invention as blocking agents for amino acids andpeptides is that they can be cleaved under mild conditions. Anotherfeature is that the conditions of cleavage can be varied, depending uponthe X₁ and X₂ substituents on the 2-propenyloxycarbonyl group. Thus, itis possible to remove other protecting groups present, e.g., acidprotecting groups, under a variety of conditions specifically withoutaffecting the 2-propenyloxycarbonyl groups which may be present in themolecule. For example, these other protecting groups can be cleavedunder acidic conditions without cleaving the protecting groups of thepresent invention.

The 2-propenyl carbamate protecting groups of the present invention arereadily cleaved by treatment of the protected amine (2-propenylcarbamate) with a nucleophile. For the purpose of this disclosure, anucleophile is an electron-rich atom, i.e., an atom which can donate anelectron pair, which tends to attack a carbon nucleus but does not actas a Bronsted Lowry base. The nucleophile as defined herein is anucleophile which is used for nucleophilic addition across a double bondand behaves in a manner similar to that described in Schemes III and IVherein below.

The general mechanism for cleavage of the 2-propenyl carbamates toprovide the free amine is believed to be a Michael-type addition to adouble bond, as shown in scheme III: ##STR26## The nucleophile isbelieved to attack at the terminal carbon atom of the propenyl group(Michael acceptor) forming a zwitterion which can eliminate the OCNR₇anion and H⁺ to form an alkene-amine and the amide (15) afterprotonation. Rearrangement and loss of CO₂ will furnish the free amine11.

The nucleophiles which will function in concert with this invention musthave an active hydrogen atom, i.e., a hydrogen atom attached to thenucleophilic atom.

It is preferred that the nucleophile is a simple amine. It is especiallypreferred that the simple amine is a primary or secondary of the formulaHNR₅ R₆ wherein R₅ and R₆ are independently hydrogen, lower alkyl orsubstituted lower alkyl, the lower alkyl being substituted with OH, CH₃,or CH₂ CH₃ or R₅ and R₆ taken together form a mono or bicyclic ringcontaining from 4 to 10 ring carbon atoms and 1 or 2 heteroatomsselected from the group consisting of nitrogen, sulfur or oxygen.

Typical examples of useful amines include ethanolamine, morpholine,piperidine, diethylamine, 2,6-dimethylpiperidine, piperazine, diethylamine and ethylamine and the like.

An organo mercaptan can also be used as a nucleophile, e.g., alkylmercaptans, cycloalkyl mercaptans, aryl mercaptan or aralkyl mercaptans.The most preferred mercaptan is benzyl mercaptan.

The nucleophile can be added as a free compound or as an insolublereagent attached to a solid support i.e., polystyrene or silica dioxide.These are represented by the formula:

    P-[alk]-NuH

wherein P is an organic polymer as defined hereinabove or a polymerhaving the formula [SiO₂ ]n; alk is a chemical bond, alkyl or aroylchain having from about one to about ten carbon atoms and Nu-H is anucleophile as defined hereinabove.

A preferred insoluble reagent in the silica based piperizine reagent 17:##STR27##

Another useful nucleophile is benzylmercaptan as shown in Scheme IV.##STR28## In this scheme the thio-group reacts in a Michael fashion toremove the Bspoc protecting group.

The enormous reactivity of the 2-propenyloxy carbonyl group might leadone to expect an insuperable problem as far as synthetic applicationsare concerned since even amino acid esters can effect deblocking.However, this is not the case. As shown by the clean conversion of thechloroformates to protected carbamates, the carbonyl group is much moreelectrophilic than the double bond so that competing attack at thelatter does not occur. Similarly no difficulties are experienced duringcoupling of Bspoc amino acids with amino acid esters during theformation of peptide bonds.

Even the DCC method for peptide synthesis is successful, although thebest results are achieved using the acid chlorides. HPLC and GC analysisshowed that these coupling reactions occurred without significantracemization (<0.1%) of the amino acids.

Deblocking of the Bspoc function by means of the insoluble silica-basedpiperazine reagent 17 is also exceptionally rapid and leads to 100%scavenging of the Bspoc ##STR29## fragment. Such rapid and cleanreactions promise general applicability for the use of 2-propenyloxycarbonyl (Michael-based systems) protecting groups in two-support,inverse Merrifield solid phase peptide synthesis. The inverse Merrifieldsolid phase synthesis is described in U.S. Pat. No. 4,623,484,incorporated herein by reference.

Typical reaction apparatus useful for solid phase peptide synthesis(SPPS) are polypropylene vials or flasks which can be subjected tovortex mixing or shaking. These flasks are often equipped with a frittedglass filter to remove excess liquid solvents and reagents by usingpressure or suction filtration. Use of these types of flasks willminimize handling of the solid support(s).

Other apparatus useful for SPPS are columns packed with solid supports.Solid supports which function in SPPS are disclosed hereinabove. Thereare two methods in general use which employ columns. One, the Merrifieldmethod, employs the solid support for attachment of the amino acid orpeptide residues. This method employs N-protected amino acids asbuilding blocks which are added to an amino acid or peptide residueattached to the solid support at the carbonyl (acid) end of themolecule. After the peptide bond has been formed, the protecting groupis removed and the cycle repeated. When a peptide having the desiredsequence has been synthesized, it is then removed from the support.

The second method, inverse Merrifield, employs reagents attached tosolid supports in a series of columns. The amino acid or peptide residueis passed through these columns in series to form the desired amino acidsequence. (See U.S. Pat. No. 4,623,484).

Michael-based systems as described herein can be controlled by the useof substituents at the vinyl-positions in addition to manipulation ofthe nature of the electron-withdrawing group (EWG). Thus the presence ofone or two substituents on X₁ and X₂ in compounds of Formula 1a shouldserve to slow down ##STR30## the deprotecting process, should it benecessary to protect against any tendency toward premature deprotection(avoidance of side reactions). Such derivatives are also expected to bemore stable in solvents, such as DMF, in which certain of theunsubstituted 2-propenyloxy carbamates may not be usable due to slowdegradation. Additional selectivity is possible via the use of hindereddeblocking agents, e.g., methylated piperidines. The relative rate ofdeblocking various

protecting groups of the present invention are indicated in Tables I,II, and III hereinbelow.

                  TABLE I                                                         ______________________________________                                         ##STR31##                                                                    R           Time for Complete Reaction, hrs.                                  ______________________________________                                        COOEt       2.8                                                               SOC.sub.6 H.sub.5                                                                         incomplete after 7 days                                           SO.sub.2 CMe.sub.3                                                                        0.8                                                               SO.sub.2 C.sub.6 H.sub.5                                                                  0.4                                                               ______________________________________                                    

                  TABLE II                                                        ______________________________________                                         ##STR32##                                                                    B           Time for Complete Reaction, hrs.                                  ______________________________________                                         ##STR33##  instantaneous                                                      ##STR34##  0.8                                                                ##STR35##  incomplete after 72 hours                                         ______________________________________                                    

                  TABLE III                                                       ______________________________________                                         ##STR36##                                                                    R     X.sub.1   X.sub.2 Time for Complete Reaction, min.                      ______________________________________                                        phenyl                                                                              H         phenyl  38                                                    phenyl                                                                              phenyl    H       20                                                    phenyl                                                                              phenyl    phenyl  stable after 3 days                                   phenyl                                                                              H         H       instantaneous                                         ______________________________________                                    

It should be noted that in addition to their applicability to inverseMerrifield synthesis, the various Michael-based protecting groupsdescribed herein can be used in classical Merrifield solid phase peptidesynthesis in place of FMOC protection. In such cases the use of Bspocamino acid chlorides, pentafluorophenyl or HOBt esters or the BOPreagent allow rapid coupling reactions. Increased solubility of all keyreagents is observed. Additional advantages of such a substitutioninclude drastic lowering of the time required to assemble a long peptidechains and lessening of side reactions. These groups can also besubstituted for base-sensitive functions (FMOC, etc.) in ordinarysolution synthesis, both single-step and repetitive, and as protectantsfor DNA coupling reactions.

EXAMPLES

The invention will now be illustrated by examples. The examples are notintended to be limiting of the scope of the present invention. Inconjunction with the general and detailed description above, theexamples provide further understanding of the present invention andoutlines a synthesis of a preferred embodiment of the invention.

The following examples represent preferred embodiments of thecompositions of the invention and methods for carrying out the blockingand deblocking of amides as can be applied to peptide and polypeptidesynthesis. The starting materials for the examples whose method ofpreparation are not indicated, are commercially available compoundswhich would be available from chemical supply houses well known to theart such as Aldrich Chemical Co.

Example 1 t-Butyl_Allyl Sulfide

To a solution of 350 mL of anhydrous ethanol maintained under nitrogenwas slowly added 22.99 g (1 mol) of sodium spheres. The sodium dissolvedwithin 90 minutes, and to the resulting sodium ethoxide solution wasadded 90.19 g (1 mol) of t-butyl mercaptan with mechanical stirring.Allyl bromide (120.98 g; 1 mol) was then added dropwise to themechanically stirred sodium t-butyl thiolate solution. After theaddition was complete, the mixture was refluxed for 10 minutes, thesolution allowed to cool, the precipitated sodium bromide filtered, andthe ethanol removed by distillation at atmospheric pressure. The residuewas diluted with 200 mL of water, and the layers separated. The aqueouslayer was extracted with five 40-mL portions of ether. The combinedorganic layers were extracted with 150 mL of water, the organic layerdried over MgSO₄, filtered, and the solvent removed in vacuo from awater bath at 45° C. to give a yellow liquid. Distillation through a0.8×15-cm fractionating column gave 56.16 g (45%) of the sulfide as acolorless liquid, bp 139°-141° C.; IR (neat), cm⁻¹ 3090, 2960 1635,1455, 1360, 1160, 985, 915; ¹ H NMR (CDCl₃) 1.35 (s, 9H, t-butyl), 3.20(d, 2H, CH₂), 4.90-6.25 (m 3H, vinyl).

Example 2 1,3-Dibromo-2-(t-butylsulfonyl) Propane

To a stirred solution of 17.37 g (0.13 mol) of t-butyl allyl sulfide in133 mL of CCl₄ at -24° C. (CCl₄ /dry ice) was added dropwise a solutionof 21.33 g (0.13 mol) of Br₂ in 67 mL of CCl₄. A yellow solidprecipitated during the addition. The mixture was warmed to roomtemperature and stirred for 10 minutes following complete solution ofthe yellow solid. The resulting solution was poured into a mixture of55.50 g (0.27 mol) of 85% m-chloroperbenzoic acid in 490 mL of CH₂ Cl₂kept at -24° C., and the mixture stirred for 30 minutes at thistemperature. The cooling bath was then removed and the mixture stirredat room temperature overnight. The precipitated m-chlorobenzoic acid wasfiltered and the filtrate washed with three 200-mL portions of saturatedNaHCO₃, followed by 200 mL of water. The organic layer was dried overMgSO₄, filtered, and the solvent removed in vacuo from a water bath at45° C. The crude product was recrystallized from 20% EtOAc/Skelly B togive 32.02 g (75%) of the dibromide, mp 139°-140° C.; IR (KBr), cm⁻¹2980, 1470, 1365, 1285, 1105, 860, 840, 685; ¹ H NMR (CDCl₃) 1.45 (S,9H, t-butyl), 3.80-4.00 (m, 5H, CH and CH₂).

Example 3 2-(t-Butylsulfonyl)-2-propenyl Bromide

A mixture of 16.78 g (0.052 mol) of 1,3-dibromo-2-(t-butylsulfonyl)propane and 14 mL (0.12 mol) of 2,6-lutidine in 55 mL of CH₂ Cl₂ wasrefluxed for 75 minutes. The solution was allowed to cool to roomtemperature and extracted with three 80-mL portions of 5% HCl followedby 80 mL of water. The organic layer was dried over MgSO₄, filtered, andthe solvent removed in vacuo from a water bath at 45° C. to give 11.46 g(91%) of the allyl bromide as a white solid, mp 40.5°-42.0° C., whichwas used without further purification; IR (KBr) 2980 cm⁻¹,1480, 1395,1230, 1100, 970, 730, 640; ¹ H NMR (CDCl₃) δ1.40 (s, 9H, t-butyl), 4.30(s, 2H CH₂ Br), 6.50 (s, 2H, vinyl).

Example 4 2-(t-Butylsulfonyl-2-propenyl Alcohol

A mixture of 8.55 g (35.3 mmol) of 2-(t-butylsulfonyl)-2-propenylbromide and 5.31 g (78.1 mmol) of sodium formate in 150 mL of methanolwas refluxed overnight. The solution was allowed to cool andconcentrated to 50 mL with the aid of a water aspirator, resulting inthe precipitation of excess sodium formate. The residue was diluted with150 mL of water and extracted with five 50-mL portions of CH₂ Cl₂. Theorganic layer was dried over MgSO₄, filtered, and the solvent removed invacuo from a water bath at 45° C. The crude product was recrystallizedfrom 15% EtOAc/Skelly F to give 4.30 g (68%) of the alcohol as acolorless solid, mp 53.5°-54.5° C.; IR (KBr), cm⁻¹ 3470, 3120, 3000,1450, 1370, 1270, 1095, 1050, 960, 900, 800, 750, 630; ¹ H NMR (CDCl₃)δ1.39 (s, 9H, t-butyl), 2.57 (t, 1H, OH), 4.56 (d, 2H CH₂ O), 6.30 (s,1H, vinyl), 6.31 (s, 1H, vinyl).

Anal. Calcd for C₇ H₁₄ O₃ S: C, 47.17; H, 7.92; S. 17.99. Found: C,47.07; H, 7.95; S, 17.70.

Example 5 2-(t-Butylsulfonyl)-2-propenyl Chloroformate

To a solution of 6.67 g (37.4 mmol) of 2-(t-butylsulfonyl)-2-propenylalcohol in 27 mL of dry THF at 0° C. was added in one portion 27 mL ofphosgene. The solution was stirred for 1 hour at 0° C. and allowed tostand at room temperature overnight. Excess phosgene and solvent wereremoved under reduced pressure. The crude product was recrystallizedfrom 25% ether/Skelly B to give 8.23 g (91%) of the chloroformate as acolorless solid, mp 56.5-57.7; IR (KBr) cm⁻¹ 2980, 1755, 1430, 1380,1290, 1140, 1100, 965, 915, 810, 750, 680, 630; ¹ H NMR (CDCl₃) δ1.41(s, 9H, t-butyl), 5.11 (s, 2H, CH₂ O), 6.37 (s, 1H, vinyl), 6.47 (s, 1H,vinyl).

Anal. Calcd for C₈ H₁₃ ClO₄ S: C, 39.92; H, 5.44; S, 3.32. Found: C,40.10; H, 5.40; S, 13.07.

Example 6 2-(t-Butylsulfonyl)-2-propenyl N-p-Chlorophenyl Carbamate

To a solution of 0.24 g (1.0 mmol) of 2-(1-butylsulfonyl)-2-propenylchloroformate in 3 mL of benzene at 0° C. was added dropwise 0.26 g (2.0mmol) of p-chloroaniline 3 mL of benzene. A white precipitate separatedalmost immediately. After the addition was complete the mixture wasstirred at 0° C. for 10 minutes and for 2 hours at room temperature. Themixture was then diluted with 15 mL of benzene and extracted with two15-mL portions of 5% HCl, followed by 15 mL of water. The organic layerwas dried over MgSO₄, filtered, and the solvent removed in vacuo from awater bath at 45° C. The crude product was recrystallized from 20%EtOAc/Skelly B to give 0.26 g (79%) of the urethane, mp 124°-125° C. Thesame compound was obtained in 85% yield by treatment of2-(1-butylsulfonyl)-2-propenyl alcohol with p-chlorophenyl isocyanate inrefluxing benzene; IR (KBr) cm⁻¹ 3340, 3120, 2980, 1730, 1600, 1490,1430, 1280, 1210, 1070, 975, 915, 830, 750, 620; ¹ H NMR (CDCl₃) δ1.4(s, 9H, t-butyl), 4.0 (t, J=1 Hz, 2H, CH₂ O) 6.3 (s, 1H, vinyl), 6.35(s, 1H, vinyl), 7.15-7.5 (m, 5H, phenyl and NH).

Anal. Calcd. for C₁₄ H₁₈ ClNO₄ S: C, 50.68; H, 5.47; N, 4.22. Found: C,50.46; H, 5.47; N, 4.28.

Example 7 2-Phenylthio-2-propenyl Alcohol

To a stirred solution of 36.0 g (0.64 mol) of propargyl alcohol and 0.12g (1.8 mmol) of powdered potassium hydroxide, was added dropwise at 125°C. over 30 minutes, 60.0 g (0.54 mol) of thiophenol. The mixture wasstirred for an additional 90 minutes, and allowed to cool to roomtemperature. The brown solution was diluted with 200 mL of ether, andextracted with three 100-mL portions of 2N sodium hydroxide, and two100-mL portions of water. The organic phase was dried over MgSO₄,filtered, and the solvent removed in vacuo from a water bath at 45° C.to give 90.4 g of a brown liquid, which, according to NMR analysis,contained 34% of the desired isomer. The mixture was fractionallydistilled through a 0.8×20-cm column packed with glass helices to give29.5 g of a colorless liquid, which by NMR analysis contained 67% of thedesired isomer, bp 109°-116° C./1.2 Torr. This liquid waschromatographed on silica gel (100-200 mesh, 50 g/gram of compound) with20% EtOAc/Skelly B as eluant, to give 16.4 g (18%) of the sulfide as acolorless liquid; IR (neat) cm⁻¹ 3360, 1610, 1580, 1470, 1430, 1040,740, 690; ¹ H NMR (CDCl₃) δ3.70 (t, 1H, OH), 4.10 (d, 2H, CH₂), 5.2 (t,J=1 Hz, 1H, vinyl), 5.55 (t, J=1 Hz, 1H, vinyl), 7.15-7.55 (m, 5H,phenyl).

Example 8 2-(Phenylsulfonyl)-2-propenyl Alcohol

A mixture of 5.03 g (30.3 mmol) of 2-(phenylthio)-2-propenyl alcohol and12.74 g (62.7 mmol) of 85% m-chloroperbenzoic acid in 250 mL of CH₂ Cl₂was stirred overnight at room temperature. The mixture was extractedwith three 100-mL portions of saturated NaHCO₃, followed by 100 mL ofwater. The organic layer was dried over MgSO₄, filtered, and the solventremoved in vacuo from a water bath at 45° C. The residue waschromatographed on silica gel (100-200 mesh, 50 g/gram of compound) with40% EtOAc/Skelly B as eluant, to give 4.30 g (72%) of the sulfone as acolorless oil; IR (neat) cm⁻¹ 3500, 1580, 1440, 1300, 1170, 1130, 1050,950, 900, 750, 690; ¹ H NMR (CDCl₃) δ3.70 (bs, 1H, OH), 4.20 (bs, 2H,CH₂) 6.05 (bs, 1H, vinyl), 6.35 (bs, 1H, vinyl) 7.30-7.95 (m, 5H,phenyl).

Anal. Calcd for C₉ H₁₀ O₃ S: C, 54.53; H, 5.08; S. 16.17. Found: C,54.57; H, 5.13; S, 16.02.

Example 9 2-(Phenylsulfonyl)-2-propenyl N-p-Chlorophenyl Carbamate

A solution of 3.38 g (17.1 mmol) of 2-(phenylsulfonyl)-2-propenylalcohol and 2.62 g (17.1 mmol) of p-chlorophenyl isocyanate in 15 mL ofbenzene was refluxed overnight. The solvent was removed in vacuo from awater bath at 45° C. to give a solid which was recrystallized twice fromCCl₄ to give 4.25 g (71%) of the urethane, mp 104°-106° C.; IR (KBr)cm⁻¹ 3320, 1730, 1600, 1530, 1300, 1215, 1065, 960, 820, 750, 680; ¹ HNMR (CDCl₃) δ4.85 (bs 2H, CH₂), 6.16 (bs, 1H, vinyl), 6.50 (bs, 1H,vinyl), 7.05-8.00 (m, 10H, phenyl and NH).

Anal. Calcd for C₁₆ H₁₄ ClNO₄ S: C, 54.63; H, 4.01; N, 3.98. Found: C,54.54; H, 3.99; N, 4.05.

Example 10 2-(Methylsulfonyl)ethyl N-p-Chlorophenyl Carbamate

A solution of 2.06 g (16.6 mmol) of 2-(methylsulfonyl)ethyl alcohol and2.55 g (16.6 mmol) of p-chlorophenyl isocyanate in 15 mL of benzene wasrefluxed for 30 minutes. The solvent was removed in vacuo from a waterbath at 45° C. to give a solid which was recrystallized from CHC₁₃ togive 2.98 g (65%) of the urethane, mp 147°-147.5° C.; IR (KBr) 3360cm⁻¹, 1720, 1600, 1490, 1310, 1230, 1130, 1070, 830, 760; ¹ H NMR(DMSO-d₆ -CDCl₃) δ3.0 (s , 3H, CH₃), 3.40 (t, 2H, CH₂ SO₂), 4.60 (t, 2H,CH₂ O), 7.15-7.55 (m, 4H, phenyl), 9.20 (bs, 1H, NH).

Anal. Calcd for C₁₀ H₁₂ ClNO₄ S: C, 43.25; H, 4.36; N, 5.04. Found: C,43.16; H, 4.14; N, 4.99.

Example 11 2-Carboethoxy-2-propenyl Alcohol

To a stirred solution of 12.07 g (53.8 mmol) of triethyl phosphonacetateand 21 mL of 35-40% aqueous formaldehyde at room temperature was addeddropwise a solution of 13.2 g (95.5 mmol) of K₂ CO₃ in 50 mL of water.The temperature of the reaction mixture rose to 48° C. over the courseof the addition. After the addition was complete, the mixture wasstirred for 1 hour, quenched with 22 mL of saturated NH₄ Cl solution,and extracted with three 25-mL portions of ether. The organic layer wasdried over Na₂ SO₄, filtered, and the solvent removed in vacuo from awater bath at 45° C. to give a colorless liquid which was distilled togive 4.57 g (65%) of the colorless alcohol, bp 60°-65° C./0.9 Torr; IR(neat) cm⁻¹ 3450, 1710, 1635, 1450, 1400, 1300, 1260, 1160, 1050, 945,820; ¹ H NMR (CDCl₃) δ1.30 (t, 3H, CH₃), 3.5-4.5 (m, 5H, CH₂ OH and CO₂CH₂), 5.90 (bs, 1H, vinyl), 6.25 (bs, 1H, vinyl).

Example 12 2-Carboethoxy-2-propenyl N-p-Chlorophenyl Carbamate

A solution of 2.12 g (16.3 mmol) of 2-(carboethoxy)-2-propenyl alcoholand 2.50 g (16.3 mmol) of p-chlorophenyl isocyanate in 15 mL of benzenewas refluxed overnight. The solvent was removed in vacuo from a waterbath at 45° C. to give a solid which was recrystallized from CCl₄ togive 2.99 g (65%) of the urethane, mp 93.0°-93.5° C.; IR (KBr) cm⁻¹3360, 1720, 1600, 1525, 1390, 1310, 1220, 1170, 1060; ¹ H NMR (DMSO-d₆/CDCl₃) δ1.25 (t, 3H, CH₃), 4.25 (q, 2H, CO₂ CH₂), 4.90 (s, 2H, CH₂ O),5.90 (bs, 1H, vinyl), 6.35 (bs, 1H, vinyl), 7.15-7.50 (m, 4H, phenyl),8.0 (bs, 1H, NH).

Anal. Calcd. for C₁₃ H₁₄ ClNO₄ : C, 55.04; H, 4.97; N, 4.94. Found: C,54.89; H, 4.69; N, 4.89.

Example 13 2-(Phenylsulfinyl)-2-propenyl Alcohol

To a stirred solution of 0.91 g (5.5 mmol) of 2-(phenylthio)-2-propenylalcohol in 60 mL of CH₂ Cl₂ at -78° C. was added 1.11 g (5.5 mmol) of85% m-chloroperbenzoic acid. The reaction mixture was stirred for 1 hourat -78° C. The cooling bath was removed and the mixture allowed to warmto room temperature. The mixture was filtered, and then extracted withthree 50-mL portions of saturated NaHCO₃. The organic layer was driedover MgSO₄, filtered, and the solvent removed in vacuo from a water bathat 45° C. The residue was flash chromatographed on silica gel (230-400mesh, 4×12-cm packed column) with 80% EtOAc/Skelly B as eluant, to give0.57 g (57%) of the sulfoxide as a colorless oil; IR (neat) cm¹ 3360,1440, 1030, 990, 930, 750, 690; ¹ H NMR (CDCl₃) δ4.00 (s, 1H, allylic),4.15 (s, 1H, allylic), 4.40 (bs, 1H, OH), 5.90 (t, J=1 Hz, 1H, vinyl),6.05 (s, 1H, vinyl), 7.35-7.80 (m, 5H, phenyl).

Example 14 2-(Phenylsulfinyl)-2-propenyl N-p-Chlorophenyl Carbamate

A solution of 0.57 g (3.1 mmol) of 2-(phenylsulfinyl)-2-propenyl alcoholand 0.48 g (3.1 mmol) of p-chlorophenyl isocyanate in 10 mL of benzenewas refluxed overnight. The solvent was removed in vacuo from a waterbath at 45° C. to give a brown oil which was recrystallized from CCl₄/Skelly B to give 0.72 g (69%) of the urethane, mp 106°-107.5° C.; IR(KBr) cm⁻¹ 3240, 1730, 1600, 1545, 1490, 1310, 1220, 1030, 745, 680; ¹ HNMR (CDCl₃) δ4.65 (s, 1H, allylic), 4.70 (s, 1H, allylic), 6.00 (s, 1H,vinyl), 6.30 (s, 1H, vinyl), 7.10-7.85 (m, 10H, phenyl and NH).

Anal. Calcd for C₁₆ H₁₄ ClNO₃ S: C, 57.23; H, 4.20; N, 4.17. Found: C,56.95; H, 4.14; N, 4.10.

Example 15t-Butyl-2-(t-Butylsulfonyl)-2-propenyloxycarbonyl-L-phenylalaninate

To a stirred solution of 0.185 g (0.768 mmol) of2-(t-butylsulfonyl)-2-propenyl chloroformate in 2 mL of benzene at 0° C.was added dropwise a solution of 0.34 g (1.53 retool) of t-butylL-phenylalaninate in 5 mL of benzene. Upon addition, a white precipitatebegan to separate. Upon completion of the addition, the slurry wasstirred at room temperature for 30 minutes, poured into 15 mL of etherand washed with three 15-mL portions of 5% HCl, and 15 Ml of water. Theorganic layer was dried over MgSO₄ , filtered, and the solvent removedin vacuo from a water bath at 45° C. The resulting oil wasrecrystallized from 20% ether/pentane to give 0.23 g (70%) of thecolorless ester, mp 67°-69° C.; IR (KBr) cm⁻¹ 3410, 2980, 1715, 1510,1365, 1290, 1155, 1095, 1060, 940, 750, 700, 625; ¹ H NMR (CDCl₃) δ1.45(s, 9H, t-butyl), 1.50 (s, 9H, t-butyl), 3.12 (m, 2H, benzyl), 4.56 (q,1H, CH), 4.90 (s, 2H, CH₂ O), 5.38 (d, 1H, NH), 6.14 (s, 1H, vinyl),6.29 (s, 1H, vinyl), 7.15-7.40 (m, 5H, Phenyl); [α]_(D) ²⁸ +25.4° (c=1CH₂ Cl₂), also, [α]₅₄₆ ²⁸ +30.9 (c=1, CH₂ Cl₂).

Anal. Calcd for C₂₁ H₃₁ NO₆ S: C, 59.27; H, 7.34; N, 3.29. Found: C,59.31; H, 7.45; N, 3.23.

Example 16 Methyl2-(t-Butylsulfonyl)-2-propenyloxycarbonyl-L-phenylalaninate

A mixture of 0.507 g (2.11 mmol) of 2-(t-butylsulfonyl)-2-propenylchloroformate and 0.454 g (2.11 mmol) of methyl L-phenylalaninatehydrochloride in 15 mL of CH₂ Cl₂ was stirred in the presence of 25 mLof 5% NaHCO₃ at room temperature for 4.25 hours. The aqueous phase wasseparated, and the organic phase was washed with two 30-mL portions of5% HCl. The organic phase was dried over MgSO₄, filtered, and thesolvent removed in vacuo from a water bath at 45° C. The crude productwas recrystallized from 20% EtOAc/Skelly F to give 0.61 g (75%) of themethyl ester, mp 63°-64° C.; IR (KBr) cm⁻¹ 3390, 1755, 1715, 1515, 1290,1225, 1100, 1065, 945, 750, 700; ¹ H NMR (CDCl₃) δ1.39 (s, 9H, t-butyl),3.13, (m, 2H, benzyl), 3.75 (s, 3H, OCH₃), 4.68 (q, 1H, CH), 4.88 (s,2H, CH₂ O), 5.32 (d, 1H, NH), 6.11, (s, 1H, vinyl), 6.26 (s, 1H, vinyl),7.10-7.40 (m, 5H, phenyl); 1 [α]_(D) ²³ +33.3° (c=1, CHCl₃), also [α]₅₄₆²³ +40.4° (c=1, CHCl₃).

Anal. Calcd for C₁₈ H₂₅ NO₆ S: C, 56.38; H, 6.57; N, 3.65. Found: C,56.68; H, 6.24; N, 3.64.

Example 17 2-(t-Butylsulfonyl)-2-propenyloxycarbonyl-L-phenylalanine

A solution of 4.57 g (19.0 mmol) of 2-(t-butylsulfonyl)-2-propenylchloroformate and 5.64 g (18.6 mmol) of t-butyl L-phenylalaninatehydrophosphite in 90 mL of CH₂ Cl₂ was stirred in the presence of 165 mLof 5% NaHCO₃ at room temperature for 2 hours. The aqueous phase wasseparated, and the organic phase washed with three 75-mL portions of 5%HCl. The organic phase was dried over MgSO₄, filtered, and the solventremoved in vacuo from a water bath at 45° C. The resulting oil wasdissolved in 36 mL of 50% CH₂ Cl₂ /triflouroacetic acid, and thesolution stirred at room temperature for (91%) of the colorless acid, mp88.0°-89.5° C.; IR (KBr) cm⁻¹ 3270, 1760 1690, 1520, 1290, 1200, 1100,1060, 960, 755, 700, 630; ¹ H NMR (CDCl₃) 1.40 (s, 9H, t-butyl), 3.20(m, 2H, benzyl), 4.75 (q, 1H, CH), 4.90 (s, 2H, CH₂ O), 5.35 (d, 1H,NH), 6.15 (s, 1H, vinyl), 6.32 (s, ¹ H, vinyl), 7.15-7.40 (m, 5H,phenyl); [α]_(D) ²⁴ -31.0° (c=0.5, DMF), also [α]₅₄₆ ²⁴ -37.5° (c=0.5DMF).

Anal. Calcd for C₁₇ H₂₃ NO₆ S: C, 55.27; H, 6.27; N, 3.79. Found: C,55.02; H, 6.47; N, 3.71.

Example 18 2-(t-Butylsulfonyl)-2-propenyloxycarbonyl-L-phenylalanylChloride

To a stirred solution of 2.50 g (6.77 mmol) of2-(t-butylsulfonyl)-2-propenyloxycarbonyl-L-phenylalanine in 15 mL ofdry CH₂ Cl₂, was added dropwise under a nitrogen atmosphere, a solutionof 4.9 mL (10 eq) of thionyl chloride in 10 mL of dry CH₂ Cl₂. Uponcompletion of the addition, the solution was refluxed for 2 hours. Thesolution was cooled to room temperature, and excess thionyl chloride andsolvent were removed under reduced pressure with the aid of a vacuumpump. The crude residue was recrystallized from 30 mL of 33% CH₂ Cl₂/pentane to give 2.13 g (82%) of the acid chloride, mp 100.0°-100.5° C.;IR (KBr) cm⁻¹ 3400, 1810, 1790, 1720, 1510, 1295, 1250, 1105, 760, 710,630; ¹ H NMR (CDCl₃) δ1.38 (s, 9H, t-butyl), 3.27 (m, 2H, benzyl), 4.88(m, 3H, CH₂ O and CH), 5.27 (d, 1H, NH), 6.10 (s, 1H, vinyl), 6.27 (s,1H, vinyl), 7.15-7.45 (m, 5H, phenyl); [α]₅₄₆ ²⁶ +15.3° (c=1, CH₂ Cl₂)also [α]_(D) ²⁶ +18.7° (c=1, CH₂ Cl₂).

Anal. Calcd for C₁₇ H₂₂ ClNO₅ S: C, 52.64; H, 5.72; N, 3.61. Found: C52.32; H, 5.39; N, 3.55.

Example 19 2-(t-Butylsulfonyl)-2-propenyloxycarbonyl Glycine

A mixture of 3.34 g (13.9 mmol) of 2-(t-butylsulfonyl)-2-propenylchloroformate and 2.95 g (13.8 mmol) of t-butyl glycinate hydrophosphitein 85 mL of CH₂ Cl₂ was stirred in the presence of 100 mL of 5% NaHCO₃at room temperature for 4 hours. The aqueous phase was separated, andthe organic phase washed with three 33-mL portions of 5% HCl. Theorganic phase was dried over MgSO₄, filtered, and the solvent removed invacuo from a water bath at 45° C. The resulting oil was dissolved in 20mL of 50% CH₂ C₂ /triflouroacetic acid, and the solution stirred at roomtemperature for 2 hours. Excess triflouroacetic acid and solvent wereremoved in vacuo from a water bath at 45° C. The resulting oil wasrecrystallized from 30% EtOAc/Skelly B to give 3.25 g (84%) of the acid,mp 105.0°-105.5° C.; IR (KBr) cm⁻¹ 3355, 1765, 1695, 1560, 1290, 1190,1100, 1050, 770; ¹ H NMR (CDCl₃) δ1.41 (s, 9H, t-butyl), 4.05 (d, 2H,CH₂), 4.94 (s, 2H, CH₂ O), 5.44 (t, 1H, NH), 6.26 (s, 1H, vinyl), 6.33(s, 1H, vinyl).

Anal. Calcd for C₁₀ H₁₇ NO₆ S: C, 43.00; H, 6.13; N, 5.01. Found: C,43.00; H, 6.03; N, 4.97.

Example 20 2-(t-Butylsulfonyl)-2-propenyloxycarbonyl Glycyl Chloride

To a stirred mixture of 0.404 g (1.45 mmol) of2-(t-butylsulfonyl)-2-propenyloxycarbonyl glycine in 4 mL of dry CH₂Cl₂, was added dropwise under a nitrogen atmosphere, a solution of 1.06mL (10 eq) of thionyl chloride in 4 mL of dry CH₂ Cl₂. Upon completionof the addition, the solution was refluxed for 1 hour. The solution wascooled to room temperature, and excess thionyl chloride and solvent wereremoved under reduced pressure with the aid of a vacuum pump. The crudeproduct was recrystallized from CH₂ Cl₂ /pentane to give 0.39 g (91%) ofthe acid chloride, mp 61.5°-62.5° C.; IR (KBr) cm⁻¹ 3400, 1800, 1740,1510, 1280, 1100, 1050, 945, 790, 750, 625; ¹ H NMR (CDCl₃) δ1.41 (s,9H, t-butyl), 4.39 (d, 2H, CH₂), 4.95 (s, 2H, CH₂ O), 5.57 (bs, 1H, NH),6.25 (s, 1H, vinyl), 6.35 (s, 1H, vinyl).

Anal. Calcd for C₁₀ H₁₆ ClNO₅ S: C, 40.34; H, 5.42; N, 4.70. Found: C,40.51; H, 5.30; N, 4.83.

Example 21 2-(t-Butylsulfonyl)-2-propenyloxycarbonyl-D-valine

A solution of 1.01 g (4.15 mmol) of 2-(t-butylsulfonyl)-2-propenylchloroformate and 0.87 g (4.15 mmol) of t-butyl D-valinate hydrochloridein 22 mL of CH₂ Cl₂ was stirred in the presence of 45 mL of saturatedNaHCO₃ for 90 minutes. The aqueous phase was separated, and the organicphase was washed with two 20-mL portions of 5% HCl. The organic phasewas dried over MgSO₄, filtered, and the solvent removed in vacuo from awater bath at 45° C. The resulting oil was dissolved in 10 mL of 50% CH₂Cl₂ /trifluoroacetic acid, and the solution stirred at room temperaturefor 90 minutes. Excess triflouroacetic acid and solvent were removed invacuo from a water bath at 45° C. The resulting oil was recrystallizedfrom ether/Skelly F to give 1.01 g (75%) of the colorless acid, mp113°-114° C.; IR (KBr) cm⁻¹ 3380, 3160, 1750, 1700, 1540, 1400, 1295,1100, 1025, 760, 665; ¹ H NMR (CDCl₃) δ0.9 (d, 3H, CH₃), 1.05 (d, 3H,CH₃), 1.4 (s, 9H, t-butyl), 2.2 (m, 1H, CH), 4.3 (d of d, 1H, CHN), 4.95(s, 2H, CH₂ O), 5.5 (d, 1H, NH), 6.25 (s, 1H, vinyl), 6.35 (s, 1H,vinyl), 11.6 (s, 1H, CO₂ H); [α]_(D) ²⁵ +3.2° (c=1, CHCl₃), also [α]₅₄₆²⁵ +3.7° (c=1, CHCl₃).

Anal. Calcd for C₁₃ H₂₃ NO₆ S: C, 48.58; H, 7.21; N, 4.36. Found: C,48.70; H, 6.99; N, 4.29.

Example 22 Methyl2-(t-Butylsulfonyl)-2-propenyloxycarbonyl-L-phenylalanyl-L-leucinate

A solution of 1.042 g (2.69 mmol) of2-(t-butyl-sulfonyl-2-propenyloxycarbonyl-L-phenylalanyl chloride and0.488 g (2.69 mmol) of methyl L-leucinate hydrochloride in 40 mL of CH₂Cl₂ was stirred with 60 mL of saturated NaHCO₃ at room temperature for45 minutes. The aqueous layer was separated, and the organic layerwashed with two 40-mL portions of 5% HCl. The organic layer was driedover MgSO₄, filtered, and the solvent removed in vacuo from a water bathat 45° C. The residue was recrystallized from 20% EtOAc/Skelly F to give1.07 g (80%) of the colorless dipeptide, mp 58°-60° C.; IR (KBr) cm⁻¹3320, 2980, 1740, 1660, 1540, 1300, 1110, 1060, 750, 700; ¹ H NMR(CDCl₃) δ0.91°-1.70 (m, 18H, aliphatic), 3.12 (d, 2H, benzyl), 3.73 (s,3H, OCH₃), 4.43 (q, 1H, CH), 4.59 (q, 1H, CH), 4.89 (s, 2H, CH₂ O), 5.46(d, 1H, NH), 6.10 (m, 2H, vinyl and NH), 6.28 (s, 1H, vinyl), 7.18-7.40(m, 5H, phenyl); [α]_(D) ²⁸ -7.1° (c=3, CHCl₃), also [α]₅₄₆ ²⁸ -8.0(c=3, CHCl₃).

Anal. Calcd for C₂₄ H₃₆ N₂ O₇ S: C, 58.04; H, 7.31; N, 5.64. Found: C,58.02; H, 7.27; N, 5.62.

Example 23 t-Butyl2-(t-Butylsulfonyl)-2-propenyloxycarbonyl-L-phenylalanyl-L-phenylalaninate

A solution of 0.564 g (1.45 mmol) of2-(t-butylsulfonyl)-2-propenyloxycarbonyl-L-phennylalanyl chloride and0.441 g (1.45 mmol) of t-butyl phenylalaninate hydrophosphite in 25 mLof CH₂ Cl₂ was stirred with 30 mL of saturated NaHCO₃ at roomtemperature for 1 hour. The aqueous phase was separated, and the organiclayer washed with two 40-mL portions of 5% HCl. The organic layer wasdried over MgSO₄, filtered, and the solvent removed in vacuo from awater bath at 45° C. The residue was recrystallized from 20%EtOAc/Skelly B to give 0.64 g (77%) of the colorless dipeptide, mp129.0°-130.0° C.; IR (KBr) cm⁻¹ 3300, 1730, 1655, 1530, 1295, 1150,1100, 750, 700; ¹ H NMR δ1.40 (s, 18H, t-butyl), 3.07 (m, 4H, benzyl),4.40 (q, 1H, CH), 4.67 (q, 1H, CH), 4.88 (s, 2H, CH₂ O), 5.35 (d, 1H,NH), 6.06 (s, 1H, vinyl), 6.18 (d, 1H, NH), 6.26 (s, 1H, vinyl),7.17-7.35 (m, 10H, phenyl); [α]_(D) ²⁹ +27.50° (c=1, CHCl₃), also [α]₅₄₆²⁹ +33.6° (c=1, CHCl₃).

Anal. Calcd for C₃₀ H₄₀ N₂ O₇ S: C, 62.92; H, 7.04; N, 4.89. Found: C,62.94; H, 7.02; N, 4.89.

Example 24 Benzyl2-(t-Butylsulfonyl)-2-propenyloxycarbonyl-L-phenylalanyl-L-leucinate

A solution of 0.773 g (1.99 mmol) of2-(t-butylsulfonyl)-2-propenyloxycarbonyl-L-phennylalanyl chloride and0.761 g (1.93 mmol) of benzyl L-leucinate hydrotosylate in 20 mL of CH₂Cl₂ was stirred in the presence of 50 mL of saturated NaHCO₃ for 20minutes. The aqueous phase was separated, and the organic phase washedwith two 25-mL portions of 5% HCl. The organic phase was dried overMgSO₄, filtered, and the solvent removed in vacuo from a water bath at45° C. The residue was recrystallized from 30% EtOAc/Skelly F to give0.80 g (73%) of the colorless dipeptide, mp 44°-46° C.; IR (KBr) cm⁻¹3320, 1735, 1660, 1530, 1300, 1110, 1055, 750, 700; ¹ H NMR (CDCl₃)δ0.9-2.1 (m, 18H, aliphatic), 3.05 (d, 2H, benzyl), 4.2-4.7 (m, 2H, CH),4.9 (s, 2H, CH₂ O), 5.15 (s, 2H, benzyl), 5.6 (d, 1H, NH), 6.1 (s, 1H,vinyl), 6.35 (m, 2H, NH, and vinyl), 7.25 (s, 5H, phenyl), 7.35 (s, 5H,phenyl); [α]_(D) ²⁸ -10.4 (c=1, CHCl₃), also [α]₅₄₆ ²⁸ -11.7° (c=1,CHCl₃).

Anal. Calcd for C₃₀ H₄₀ N₂ O₇ S: C, 62.92; H, 7.04; N, 4.89. Found: C,62.81; H, 6.92; N, 4.86.

Example 25t-Butyl-2-(t-Butylsulfonyl)-2-propenyloxycarbonyl-L-phenylalanylglycinate

A solution of 0.697 g (1.80 mmol) of2-(t-butylsulfonyl)-2-propenyloxycarbonyl-L-phenylalanyl chloride and0.371 g (1.74 mmol) of t-butyl glycinate hydrophosphite in 25 mL of CH₂Cl₂ was stirred in the presence of 40 mL of saturated NaHCO₃ for 25minutes. The aqueous phase was separated, and the organic phase waswashed with two 40-mL portions of 5% HCl. The organic phase was driedover MgSO₄, filtered, and the solvent removed in vacuo from a water bathat 45° C. The residue was recrystallized from EtOAc/Skelly B to give0.54 g(64%) of the dipeptide, mp 86.5°-87.5° C.; IR (KBr) cm⁻¹ 3380,1750, 1660, 1530, 1300, 1170, 1105, 955, 750, 710, 630; ¹ H NMR (CDCl₃)δ1.35 (s, 9H, t-butyl), 1.45 (s, 9H, t-butyl), 3.1 (m, 2H, benzyl), 3.9(d, 2H, CH₂), 4.45 (q, 1H, CH), 4.85 (s, 2H, CH₂ O), 5.7 (d, 1H, NH),6.05 (s, 1H, vinyl), 6.35 (s, 1H, vinyl), 6.5 (m, 1H, NH), 7.25 (s, 5H,phenyl); [α]_(D) ²⁶ -4.8° (c=1, CHCL₃), also [α]₅₄₆ ²⁶ -5.9° (c=1,CHCL₃).

Anal. Calcd for C₂₃ H₃₄ N₂ O₇ S: C, 57.24; H, 7.10; N, 5.80. Found: C,57.42; H, 6.99; N, 6.16.

Example 26t-Butyl-2-(t-Butylsulfonyl)-2-propenyloxycarbonyl-L-phenylalanyl-L-phenylalanyl-L-phenylalaninate

To a stirred solution of 3.45 g (3.45 mmol) of aminomethylpiperidnylsilica gel in 10 mL of CH₂ Cl₂ was added 197 mg (0.344 mmol) of t-butyl2-(t-butylsulfonyl)-2-propenyloxycarbonyl-L-phenylalanyl-L-phenylalaninate.The mixture was stirred for 20 minutes, filtered, and the silica washedwith two 10-mL portions of CH₂ Cl₂. To this CH₂ Cl₂ solution was added138 mg (0.345 mmol) of2-(t-butylsulfonyl)-2-propenyloxycarbonyl-L-phenylalanyl chloride,followed by 40 mL of saturated NaHCO₃. The reaction mixture was stirredat room temperature for 20 minutes. The phases were separated, theorganic layer was extracted with two 20-mL portions of saturated NaHCO₃,two 20-mL portions of 5% HCl, dried over MgSO₄, filtered, and thesolvent removed in vacuo from a water bath at 45° C. Recrystallizationfrom 20% EtOAc/Skelly B gave 187 mg (75%) of the tripeptide, mp97.0°-99.0° C.; IR (KBr) cm⁻¹ 3300, 2980, 1730, 1660, 1540, 1300, 1160,1110, 1060, 760, 710; ¹ H NMR (CDCl₃) 1.33 (s, 18H, t-butyl), 3.00 (d,6H, benzyl), 4.33-4.85 (m, 5H, CH₂ O and CH), 5.50-6.75 (m, 5H, NH andvinyl), 7.23 (bs, 15H phenyl); [α]_(D) ²⁵ +8.1° (c=0.6, CHCl₃), also[α]₅₄₆ ²⁵ +11.2° (c=0.6, CHCl₃).

Anal. Calcd for C₃₉ H₄₉ O₈ N₃ S: C, 65.07; H, 6.86; N, 5.84. Found: C,64.99; H, 6.84; N, 5.86.

Example 27 trans-Phenylβ-Styryl Sulfide

To a stirred solution of 14.0 g (0.137 mol) of freshly distilledphenylacetylene at 0° C. was added dropwise 15.1 g (0.137 mol) ofthiophenol. The solution was stirred at room temperature overnight. Thereaction mixture was distilled to give 22.2 g (76%) of a colorlessliquid, bp 177°-181° C./5 Torr. NMR analysis showed a trans/cis-ratio of80/20. ¹ H NMR (CDCl₃) δ6.53 (d, J=1, Hz, 1H, cis-vinyl), 6.81 (d, J=2Hz 1H, trans-vinyl).

Example 28 trans-Phenylβ-Styryl Sulfone

To a slightly frozen mixture of 8.17 g (38.5 mmol) of an 80/20trans-cis-mixture of phenylβ-styryl sulfide in 160 mL of acetic acid wasadded dropwise 16 mL of 30% hydrogen peroxide. The solution was refluxedfor 1 hour, poured on crushed ice to give an oil which soon solidified,and was filtered. The crude solid was dissolved in 100 mL of CH₂ Cl₂,dried over MgSO₄, filtered, and the solvent removed in vacuo from awater bath at 45° C. to give 6.64 g (71%) of a solid which containedapproximately 15% of the cis-isomer as determined by 1H-NMR analysis.Recrystallization from 30% EtOAc/Skelly B gave 3.2 g (34%) of the purecolorless sulfone, mp 72.5°-73.5° C.; ¹ H NMR (CDCl₃) 6.8 (d, J=15 Hz;1H, vinyl), 7.2-8.1 (m, 11H, vinyl and phenyl).

Example 29 (E)-3-Phenyl-2-(phenylsulfonyl)-2-propenyl Alcohol

To a stirred solution of 2.0 g (8.2 mmol) of trans-phenyl β-styrylsulfone in 50 mL of dry THF at -78° C. was added dropwise under anitrogen atmosphere 6.0 mL (8.4 mmol) of 1.4 M n-BuLi within 5 minutes.The reddish-purple solution was stirred at -78° C. for 30 minutes.Gaseous formaldehyde, generated by heating paraformaldehyde at 170° C.,was passed through a 5-mm tube into the reaction mixture with the aid ofa slow stream of nitrogen at -78° C. for 45 minutes. The mixture wasallowed to come to room temperature over a period of 30 minutes whilecontinuing to pass formaldehyde through the reaction mixture until apale yellow solution was obtained. The reaction was quenched with 75 mLof 5% HCl and extracted with 50 mL of ether. The organic layer waswashed with two 50-mL portions of water, dried over MgSO₄, filtered, andthe solvent removed in vacuo from a water bath at 45° C. to give 2.1 g(93%) of the crude alcohol as a brown oil. The oil was flashchromatographed in two 1.05 g batches on silica gel (230-400 mesh,4×19-cm column) with 50% ether/Skelly B as eluant to give 0.99 g (44%)of a light yellow solid, mp 85°-87° C. Recrystallization from 40%ether/Skelly B gave the pure colorless alcohol, mp 88°-89° C. IR (KBr)cm⁻¹ 3470, 1625, 1445, 1285, 1145, 1020, 770, 755, 735, 700, 680; ¹ HNMR (CDCl₃) δ2.63 (t, 1H, OH), 4.37 (d, 2H, CH₂ O), 7.27-8.13 (m, 11H,phenyl and vinyl).

Anal. Calcd for C₁₅ H₁₄ O₃ S: C, 65.67; H, 5.14; S, 11.69. Found: C,65.60; H, 5.12; S, 11.31.

Example 30 (E)-3-Phenyl-2-(phenylsulfonyl)-2-propenyl N-p-ChlorophenylCarbamate

A solution of 0.56 (2.04 mmol) of(E)-3-phenyl-2-(phenylsulfonyl)-2-propenyl alcohol and 0.32 g (2.08mmol) of p-chlorophenyl isocyanate in 10 mL of benzene was refluxed for120 hours. The solvent was removed in vacuo from a water bath at 45° C.The crude solid was recrystallized from 20% EtOAc/Skelly B to give 0.41g (47%) of the colorless urethane, mp 138.5°-139.5° C.; IR (KBr) cm⁻¹3320 1695 1590 1520 1305 1230 1150 1045; ¹ H NMR (CDCl₃) δ5.07 (s, 2H,CH₂ O) 6.52 (bs, 1H, NH), 7.25-8.08 (m, 14H, phenyl), 8.15 (s, 1H,vinyl).

Anal. Calcd for C₂₂ H₁₈ ClNO₄ S: C, 61.75; H, 4.24; N, 3.27. Found: C,61.54; H, 4.27; N, 3.11.

Example 31 Thiophenyl Trimethylsilyl Methane

To a stirred solution of 143 mL of 1.4M n-BuLi (0.20 mol) in 55 mL ofdry THF, was added dropwise at room temperature under a nitrogenatmosphere 24.8 g (0.20 mol) of thioanisole. Upon completion of theaddition, the yellow mixture began to reflux spontaneously. The mixturewas stirred at room temperature for 3 hours. Upon addition of 21.84 g(0.20 mol) of chlorotrimethylsilane, the mixture again began to refluxspontaneously. After stirring at room temperature overnight, the mixturewas quenched with 100 mL of 5% of HCl. The aqueous layer was separated,and the organic layer was dried over MgSO₄, filtered, and the solventremoved in vacuo from a water bath at 45° C. The crude product wasdistilled to give 19.22 g (49%) of the colorless sulfide, bp 84°-86°C./0.3 Torr; ¹ H NMR (CDCl₃) δ0.17 (s, 9H, Si(CH₃)₃), 2.13 (s, 2H, CH₂S), 7.0-7.42 (m, 5H, phenyl).

Example 32 Benzenesulfonyl Trimethylsilyl Methane

To a stirred mixture of 14.1 g (69.4 mmol) of 85% m-chloroperbenzoicacid in 300 mL of CH₂ Cl₂ at 0° C. was added dropwise 6.82 g (34.7 mmol)of thiophenyl trimethylsilyl methane. The mixture was stirred at 0° C.for 3 hours and then at room temperature overnight. The mixture wasextracted with three 75-mL portions of saturated NaHCO₃. The organiclayer was dried over MgSO₄, filtered, and the solvent removed in vacuofrom a water bath at 45° C. The crude product was Kugelrohred at 115°C./0.1 Torr to give 6.83 g (86%) of the clear sulfone; ¹ H NMR (CDCl₃)δ0.27 (s, 9H, Si(CH₃)₃), 2.8 (s, 2H, CH₂ SO₂), 7.13-8.05 (m, 5H,phenyl).

Example 33 2,2-Diphenyl-1-(phenylsulfonyl) Ethene

To a stirred solution of 2.0 g (8.76 mmol) of benzenesulfonyltrimethylsilyl methane in 20 mL of dry THF at 0° C., was added dropwiseunder a nitrogen atmosphere 6.25 mL of 1.4M n-BuLi (8.75 mmol). Thereddish-orange solution was stirred at 0° C. for 30 minutes. To thesolution was added 1.60 g (8.78 mmol) of benzophenone. The solution wasstirred at 0° C. for 2 hours, then at room temperature overnight. Thereaction mixture was diluted with 50 mL of 5% HCl, and extracted withthree 25-mL portions of water, dried over MgSO₄, filtered, and thesolvent removed in vacuo from a water bath at 45° C. The crude productwas recrystallized from 15% EtOAc/Skelly B to give 1.25 g (44%) of theslightly yellow sulfone, mp 111.0°-112.5° C.; ¹ H NMR (CDCl₃) δ7.02 (s,1H, vinyl), 7.12-7.72 (m, 15H, phenyl).

Example 34 3,3-Diphenyl-2-(phenylsulfonyl)-2-propenyl Alcohol

To a stirred solution of 1.25 g (3.90 mmol) of2,2-diphenyl-1-(phenylsulfonyl) ethene in 20 mL of dry THF at -78° C.,was added dropwise under a nitrogen atmosphere 2.8 mL of 1.4M n-BuLi(3.90 mmol). The dark black solution was stirred at -78° C. for 30minutes. Gaseous formaldehyde, generated by heating paraformaldehyde at170° C., was passed through a 5-mm tube into the reaction mixture withthe aid of a slow stream of nitrogen at -78° C. for 30 minutes. Themixture was allowed to come to room temperature over a period of 30minutes while continuing to pass formaldehyde through the reactionmixture until a pale yellow color was observed. The mixture was stirredovernight at room temperature. The mixture was quenched with 50 mL of 5%HCl, and extracted with three 25-mL portions of CH₂ Cl₂. The organiclayer was dried over MgSO₄, filtered, and the solvent removed in vacuofrom a water bath at 45° C. The resulting crude oil was flashchromatographed on silica gel (230-400 mesh, 5×16-cm column) with 30%ether/Skelly B as eluant to give 0.47 g (34%) of the colorless alcohol.In a melting point capillary the compound does not melt but decomposesabove 290° C. with blackening; IR (KBr) cm⁻¹ 3480, 3040, 1590, 1480,1440, 1370, 1280, 1130, 1020, 960, 790, 730, 700, 680, 610; ¹ H NMR(CDCl₃) δ3.47 (t, 1H, OH), 4.61 (d, 2H, CH₂ O), 6.75-7.58 (m, 15H,phenyl).

Anal. Calcd for C₁₂ H₁₈ O₃ S: C, 71.98; H, 5.18; S, 9.15. Found: C.71.97; H, 5.22; S, 9.02.

Example 35 3,3-Diphenyl-2-(phenylsulfonyl)-2-propenyl N-p-ChlorophenylCarbamate

A solution of 0.35 g (1.0 mmol) of3,3-diphenyl-2-(phenylsulfonyl)-2-propenyl alcohol and 0.15 g (1.0 mmol)of p-chlorophenyl isocyanate in 2 mL of benzene was refluxed for 18hours. The solvent was removed in vacuo from a water bath at 45° C.Recrystallization from 95% EtOAc/EtOH gave 0.38 g (78%) of the colorlessurethane. In a melting point capillary the compound does not melt butdecomposes above 250° C.; IR (KBr) cm⁻¹ 3310, 1730, 1590, 1530, 1490,1300, 1205, 1140, 1050, 825, 700, 680; ¹ H NMR (CDCl₃) 5.13 (s, 2H, CH₂O), 6.80 (bs, 1H, NH), 6.91-7.58 (m, 19H, phenyl).

Anal. Calcd for C₂₈ H₂₂ ClNO₄ S: C, 66.73; H, 4.40; N, 2.78. Found: C,66.51; H, 4.44; N, 2.54.

Example 36 cis-Phenylβ-Styryl Sulfide

To a solution of 150 mL of anhydrous ethanol maintained under nitrogenwas added 3.45 g (0.15 mol) of sodium. The sodium dissolved within 25minutes, and to the resulting sodium ethoxide solution was added 16.5 g(0.15 mol) of thiophenol. The solution was brought to reflux, and 15.0 g(0.15 mol) of phenylacetylene was added dropwise. The solution wasrefluxed overnight, cooled, and poured over crushed ice. The precipitatewas filtered, dissolved in 100 mL of CH₂ Cl₂, dried over MgSO₄,filtered, and the solvent removed in vacuo from a water bath at 45° C.The crude product was recrystallized from Skelly F to give 22.61 g (71%)of the sulfide, mp 43.0°-44.5° C.; ¹ H NMR (CDCl₃) δ6.51 (d, 2H, vinyl),7.13-7.67 (m, 10H, phenyl).

Example 37 (Z)-3-Phenyl-2-(thiophenyl)-2-propenyl Alcohol

To a solution of 1.0 g (4.7mmol) of cis-phenylβ-styryl sulfide in 20 mLof dry THF at -78° C. was added dropwise under a nitrogen atmosphere 5.0mL (7.0 mmol) of 1.4M n-BuLi within 5 minutes. The light yellow solutionwas stirred at -78° C. for 30 minutes. Gaseous formaldehyde, generatedby heating paraformaldehyde at 170° C., was passed through 5-mm tubeinto the reaction mixture with the aid of a slow steam of nitrogen at-78° C. for 3 hours. The mixture was allowed to come to room temperatureover a period of 30 minutes and stirred overnight. The mixture wasquenched with 30 mL of 5% HCl and extracted with three 25-mL portions ofCH₂ Cl₂. The organic layer was dried over MgSO₄, filtered, and thesolvent removed in vacuo from a water bath at 45° C. to give a brownoil. The oil was flash chromatographed on silica gel (230-400 mesh,4×18-cm packed column) with 20% EtOAc/Skelly B as eluant to give 0.50 g(45%) of the alcohol, mp 64.0°-65.0° C.; IR (KBr) cm⁻¹ 3240, 3140, 1580,1470, 1090, 1070, 1010, 740, 695; ¹ H NMR (CDCl₃) δ1.82 (broad, 1H, OH),4.17 (d, 2H, CH₂ O), 7.15-7.75 (m, 11H, phenyl and vinyl).

Anal. Calcd for C₁₅ H₁₄ OS: C, 74.35; H, 5.82; S, 13.23. Found: C,74.35; H, 5.90; S, 13.18.

Example 38 (Z)-3-Phenyl-2-(phenylsulfonyl)-2-propenyl Alcohol

A mixture of 0.47 g (1.94 mmol) of(Z)-3-phenyl-2-(thiophenyl)-2-propenyl alcohol and 0.79 g (3.89 mmol) of85% m-chloro-perbenzoic acid in 10 mL of CH₂ Cl₂ was stirred at roomtemperature overnight. The mixture was diluted with 40 mL of CH₂ Cl₂ andextracted with three 50-mL portions of saturated NaHCO₃. The organiclayer was dried over MgSO₄, filtered, and the solvent removed in vacuofrom a water bath at 45° C. to give a clear oil. The oil wasrecrystallized from 20% EtOAc/Skelly B to give 0.27 g (51%) of thesulfone, mp 67.5°-69.0° C.; IR (KBr) cm⁻¹ 3280, 3180, 1445, 1300, 1150,1080, 1025, 990, 750, 730, 650, 610; ¹ H NMR (CDCl₃) 2.85 (s, 1H, OH),4.67 (s, 2H, CH₂ O), 7.21-7.83 (m, 11H, phenyl and vinyl).

Anal. Calcd for C₁₅ H₁₄ O₃ S: C, 65.67; H, 5.14; S, 11.69. Found: C,65.45; H, 4.97; S, 11.82.

Example 39 (Z)-3-Phenyl-2-(phenylsulfonyl)-2-propenyl N-p-ChlorophenylCarbamate

A solution of 0.22 g (0.80 mmol) of(Z)-3-phenyl-2-(phenylsulfonyl)-2-propenyl alcohol and 0.12 g (0.78mmol) of p-chlorophenyl isocyanate in 4 mL of benzene was refluxedovernight. The solvent was removed in vacuo from a water bath at 45° C.The crude product was recrystallized from 15% EtOAc/Skelly B to give0.23 g (70%) of the urethane, mp 124.0°-125.0° C.; IR (KBr) cm⁻¹ 3320,1740, 1590, 1525, 1300, 1210, 1120, 1050, 830, 740, 690; ¹ H NMR (CDCl₃)δ5.23 (s, 2H, CH₂ O), 7.05 (bs, 1H, NH), 7.22-7.83 (m, 15H, phenyl andvinyl).

Anal. Calcd for C₂₂ H₁₈ ClNO₄ S: C, 61.75; H, 4.24; N, 3.27. Found: C,61.70; H, 4.09; N, 3.21.

Example 40 2-(Phenylsulfonyl)-2-propenyl chloroformate

Using the procedure from Example 5, 2-(phenylsulfonyl)-2-propenylalcohol can be readily converted to 2-(phenylsulfonyl)-2-propenylchloroformate.

Example 41 2-Carbethoxy-2-propenyl chloroformate

Using the procedure from Example 5, 2-carbethoxy-2-propenyl alcohol canbe readily converted to 2-carbethoxy-2-propenyl chloroformate.

Example 42 2-(Phenylsulfonyl)-2-propenyl chloroformate

Using the procedure from Example 5,2-(phenylsulfonyl)-2-propenyl alcoholcan be readily converted to 2-phenylsulfonyl)-2-propenyl chloroformate.

Example 43 (E)-3-Phenyl-2-(phenylsulfonyl)-2-propenyl chloroformate

Using the procedure from Example 5,(E)-3-phenyl-2-(phenylsulfonyl)-2-propenyl alcohol can be readilyconverted to (E)-3-phenyl-2-(phenylsulfonyl)-2-propenyl chloroformate.

Example 44 (Z)-3-Phenyl-2-(phenylsulfonyl)-2-propenyl chloroformate

Using the procedure from Example 5,(Z)-3-phenyl-2-(phenylsulfonyl)-2-propenyl alcohol can be readilyconverted to (Z)-3-phenyl-2-(phenylsulfonyl)-2-propenyl chloroformate.

Example 45 3,3-Diphenyl-2-(phenylsulfonyl)-2-propenyl chloroformate

Using the procedure from Example 5,3,3-diphenyl-2-(phenylsulfonyl)-2-propenyl alcohol can be readilyconverted to 3,3-diphenyl-2-(phenylsulfonyl)-2-propenyl chloroformate.

Example 46 Benzothiophenesulfone-2-methanol

Oxidation of 0.5 g of benzothiophene-2-methanol [F. F. Blicke and D. G.Sheets, J. Am. Chem. Soc., 71, 2856 (1949)] with 2 eqs. ofm-chloroperbenzoic acid in 20 mL methylene dichloride gave in 51% yieldthe sulfone alcohol, mp 112°-113° C.

Anal. Calcd for C₉ H₈ O₃ S: C, 55.10; H, 4.08. Found: C, 54:81; H, 4.10.

The corresponding urethane derived from p-chlorophenyl isocyanate had mp154°-56° C.

Anal. Calcd for C₁₆ H₁₂ ClNO₄ S: C, 54.94; H, 3.43; N, 4.01; Cl, 10.16.Found: C, 54.87; H, 3.48; N, 3.94; Cl, 10.35.

Example 47

Similarly, by using the procedures described herein and the appropriatestarting materials, the following compounds are prepared:

3,3-dimethyl-2-(phenylsulfonyl)-2-propenyl alcohol

3,3-dimethyl-2-(phenylsulfonyl)-2-propenyl chloroformate

Benzothiophenesulfone-2-methyl chloroformate.

Example 48 Racemization Test

Preparation of Crude Methyl2-(t-butylsulfonyl)-2-propenyloxycarbonyl-L-phenylalanyl-L-leucinate. Asolution of 71.8 mg (0.185 mmol) of2-(t-butylsulfonyl)-2-propenyloxycarbonyl-L-phenylalanyl chloride and33.6 mg of methyl L-leucinate hydrochloride in 5 mL of CH₂ Cl₂ wasstirred with 10 mL of saturated NaHCO₃ at room temperature for 2 hours.The aqueous layer was separated, and the organic layer washed with two10-mL portions of saturated NaHCO₃, and two 100 mL portions of 5% HCl.The organic layer was dried over MgSO₄, filtered, and the solventremoved in vacuo from a water bath at 45° C. to give 90 mg (98%) of thecrude dipeptide as an oil.

HPLC Analysis. A mixture of 84 mg of the crude dipeptide and 2.11 g (10eq) of piperazyl silica gel in 28 mL of CH₂ Cl₂ was stirred at roomtemperature for 15 minutes. The silica gel was filtered, and washed with15 mL of CH₂ Cl₂. The solvent was removed by means of a slow stream ofnitrogen. The deblocked dipeptide was dissolved in 5 mL of CH₂ Cl₂, andto this solution was added 37 μL (1.9 eq) of benzoyl chloride, followedby 5 mL of saturated NaHCO₃. To the reaction mixture was added 170 μL orN-methylpiperazine, and the reaction mixture stirred at room temperaturefor 15 minutes, diluted with 15 mL of CH₂ Cl₂, and the phases separated.The organic layer .was washed with three 10-mL portions of 5% HCl, two10-mL portions of saturated NaHCO₃, two 10-mL portions of water, driedover MgSO₄, filtered, and the solvent removed in vacuo from a water bath45° C. to give 43 mg (69%) of the crude Bz-Phe-Leu-OMe, mp 153.0°-156.0°C. HPLC analysis was carried out on a Waters Radial Pak 10-um silicacolumn (0.8×10 cm) using 3% 2-propanol in hexane as the mobile phase.Retention times (min) for the two diastereomeric benzoyl dipeptideesters were 15.3 (L,L) and 19.2 (D,L). Triplicate analysis showed <0.1%of the D,L diastereomer to be present.

GC Analysis. A mixture of 6 mg of the crude dipeptide and 0.302 g (20eq) of piperazyl silica gel in 2 mL of CH₂ Cl₂ was stirred at roomtemperature for 15 minutes. The silica gel was filtered, and washed with4 mL of CH₂ Cl₂. The solution was divided equally into two 2-mL PierceReactivials, and the solvent evaporated under a slow stream of nitrogen.The residue was dissolved in 1 mL of 6N HCl, flushed with nitrogen, andheated at 110° C. for 24 hours. The solvent was evaporated under a slowstream of nitrogen. The residue was dissolved in 1 mL of 2N HCl inisopropanol, flushed with nitrogen, and heated at 110° C. for 1 hour.The solvent was evaporated under a slow stream of nitrogen. The residuewas dissolved in 250 μL of ethyl acetate, and 50 μL ofpentaflouropropionic anhydride was added. The solution was flushed withnitrogen, and heated at 110° C. for 10 minutes. The solvent was removedunder a slow stream of nitrogen. The duplicate samples were dissolved in10 μL of CH₂ Cl₂. GC analysis was carried out on a ChrompackChirasil-Val-L 25 m WCOT capillary column. Triplicate analyses on thetwo samples showed 0.83% of the D-phe enantiomer present. Analysis of ablank sample of phenylalanine showed 0.81% of the D-phe enantiomer.Subtracting the amount of the D-form found in the blank showed 0.02% ofD-phe, which corresponds to 0.04% racemization for the full cyclepreparation of acid chloride, coupling, and deblocking.

Example 49 Deblocking of Bspoc-p-Chloroaniline via Benzylmercaptan

To a solution of 66.2 mg of Bspoc-Parachloroaniline in 0.4 mL ofmethanol-d₄ was added 100 mg of benzylmercaptan. Examination of the NMRspectrum before and after addition of the mercaptan showed that noreaction has occurred, To the solution was added 100 mg ofN-ethyldiisopropylamine. Immediate NMR examination of the solutionshowed that complete deblocking of the urethane had occurred with theliberation of 100% of the free p-chloroaniline. When onlyN-ethyldiisopropylamine was added to a solution of the urethane (absenceof mercaptan) NMR examination showed that no reaction occurred.

Example 50 Leucine Enkephalin

A. Standard Merrifield Method.

A polyamide or polystyrene resin functionalized with leucine in the formof a trifluoroacetic acid-sensitive benzyl ester linkage is coupled withone equivalent of Bspoc-Phe-Cl in dimethyl formamide (DMF) for 3-5 min.Deblocking is effected by 10% piperidine or morpholine in DMF for 3-5min. This is followed by treatment of the resultant peptide with oneequivalent of Bspoc-Gly-Cl and subsequent deprotection. This is followedby treatment with a second equivalent of Bspoc-Gly-Cl, Afterdeprotection the peptide is treated with an equivalent ofBspoc-Tyr(OBz)-Cl, Deprotection and removal from the resin support willfurnish leucine enkaphalin.

B. Inverse Merrifield (two polymer) System

A general procedure for the preparation of a peptide by the use ofactive esters of the polymers is as follows:

1 equivalent of leucine having a C-terminal blocking group is introducedas the amine hydrochloride or trifluoroacetate to a suspension of 40%molar excess of the polymeric active ester of Bspoc-Phe to be coupledwith the polymer in chloroform. 2 equivalents of triethylamine are addedand the mixture shaken for 15-60 minutes. The polymer is washed withchloroform; the chloroform solution is then washed with water and with acold solution of 10% NaHSO₄, and evaporated to yield the pure N-Bspocpeptide. The N-Bspoc protecting grgu_(p) is removed by polymericpiperazine in the usual manner and then the peptide is subjected to anew coupling cycle, the polymeric active ester Bspoc-Gly. After removalof the Bspoc group a second Bspoc-Gly group is coupled. This is followedby coupling with Bspoc-Tyr(OBz)-Cl . Following this procedure, theblocked enkephaline Bspoc-Tyr(OBz)-Gly-Gly-Phe-Leu-OBz may be preparedin an overall 90% or better yield.

The above preferred embodiments and examples are given to illustrate thescope and spirit of the present invention. These embodiments andexamples will make apparent, to those skilled in the art, otherembodiments and examples. These other embodiments and examples arewithin the contemplation of the present invention. Therefore, thepresent invention should be limited only by the appended claims.

What is claimed is:
 1. In a method of protecting a primary or secondaryamine functionality on an organic molecule during a chemical reactionwhich modifies a portion of the molecule other than the protected aminefunctionality, the improvement comprising:(a) reacting, prior to saidchemical reaction, the molecule with a compound of the formula:##STR37## to form a protected amine functionality; whereinR is anelectron withdrawing group; Z is a leaving group; X₁ and X₂ areindependently H, lower alkyl, aryl lower alkyl or polystyrene or R andX₁ taken together with the carbon atoms to which they are attached forma monocyclic, bicyclic or tricylic ring so that said compound has theformula: ##STR38## B is a chemical bond, CR₈ R₉, ##STR39## SO₂, SO, orS; F is a chemical bond, CR₁₂ R₁₃, SO₂, S, SO, or ##STR40## Ring G isabsent or is a mono or bicyclic fused ring containing 5 to 10 ringcarbon atoms and up to 2 ring heteroatoms wherein said ring heteroatomsare S, N, or O, with the proviso that when ring G is absent or does notcontain a ring heteroatom, then at least one of B or F is ##STR41## SO₂,SO or S; R₈, R₉, R₁₁, R₁₂ and R₁₃ are independently hydrogen or loweralkyl; b) subsequent to the conclusion of said chemical reaction,removing the protecting group from the amine functionality.
 2. Themethod of claim 1 wherein the protecting group is removed from the aminogroup by treating the amino protected organic molecule with anucleophile.
 3. The method of claim 2 wherein the nucleophile is asimple amine or organomercaptan.
 4. The method of claim 3 wherein thesimple amine is HNR₅ R₆ wherein R₅ and R₆ are independently hydrogen,unsubstituted lower alkyl or substituted lower alkyl, the lower alkylbeing substituted with OH, or CH₃ or CH₂ CH₃, or R₅ and R₆ takentogether form a ring containing 4 to 10 ring carbon atoms and up to tworing heteroatoms, wherein the heteroatoms are O, S, or N.
 5. The methodof claim 3 wherein the nucleophile is piperidine,2,6-dimethylpiperidine, piperazine, morpholine, diethylamine,ethylamine, ethanolamine or benzylmercaptan.
 6. The method of claim 3wherein the simple amine is piperidine.
 7. The method of claim 1 whereinthe compound to be protected is an α-amino acid and the chemicalreaction is the formation of a peptide bond.
 8. A method for preparing apeptide which comprises:(a) reacting a first amino acid having a freeamino group with a compound of the formula: ##STR42## to form an aminoacid having a protecting group thereon, wherein Z is a leaving group;X₁and X₂ are independently H, lower alkyl, aryl, aryl lower alkyl orpolystyrene; R is an electron withdrawing group; or R and X₁ takentogether with the carbon atoms to which they are attached form amonocyclic, bicyclic or tricyclic ring so that said compound has theformula: ##STR43## B is a chemical bond, CR₈ R₉, ##STR44## SO₂, SO or S,F is a chemical bond, CR₁₂ R₁₃, SO₂, S, SO or ##STR45## Ring G is absentor is a mono or bicyclic fused ring containing 5 to 10 ring carbon atomsand up to 2 ring heteroatoms wherein said ring heteroatoms are S, N, orO, with the proviso that when ring G is absent or does not contain aring heteroatom, then at least one of B or F is ##STR46## SO₂, SO or S;and R₈, R₉, R₁₁, R₁₂, and R₁₃ are independently hydrogen or lower alkyl;(b) reacting the product of (a) with a second amino acid or peptidehaving a free amino group; and (c) removing the protecting group fromthe product of (b).
 9. The method of claim 8 wherein the product of step(a) is reacted with an amino acid or peptide which is attached to apolystyrene.
 10. The method according to claim 1 or 8 wherein Z is halo,CN, SR₄, SAr, N₃, OAr, ##STR47## R₄ is lower alkyl, aryl or aryl loweralkyl wherein the alkyl or aryl groups are unsubstituted or mono- ordisubstituted with halide, SO₂ R₂, SOR₂, COOR₂, CHO, COR₂, CN, CF₃ orNO₂ and R₂ is lower alkyl, aryl, aryl lower alkyl or polystyrene. 11.The method according to claim 10 wherein Z is halo.
 12. The methodaccording to claim 1 or 8 wherein Z is Cl.
 13. The method according toclaim 1 or 8 wherein X₂ is hydrogen, phenyl or lower alkyl having from 1to 4 carbon atoms.
 14. The method according to claim 1 or 8 wherein X₁and X₂ are independently hydrogen, phenyl or lower alkyl having from 1to 4 carbon atoms.
 15. The method according to claim 1 or 8 wherein R isSO₂ R₂, SOR₂, COOR₂, COR₂, CHO, CONR₂ R₃, CN, CF₃, NO₂, aryl or pyridyl,and R₂ and R₃ are independently lower alkyl, aryl, aryl lower alkyl orheteroaryl.
 16. The method according to claim 15 wherein R is SO₂ R₂,SOR₂, COOR₂, COR₂, CONR₂ R₃, aryl, 2-pyridyl or 4-pyridyl.
 17. Themethod according to claim 16 wherein R is SO₂ C(CH₃)₃, SOC(CH₃)₃, SO₂ C₆H₅, SOC₆ H₅, 2-pyridyl or 4-pyridyl.
 18. The method according to claim 1or 8 wherein R and X₁ taken together with the carbon atoms to which theyare attached form the bicyclic or tricyclic ring.
 19. The methodaccording to claim 1 or 8 wherein the compound has the formula:##STR48##
 20. The method according to claim 19 wherein the compound is##STR49## wherein B is CR₈ R₉ or SO₂ ;E and D are independently CH or N;R₈ and R₉ are independently hydrogen or lower alkyl, provided that whenB is CR₈ R₉, then E or D is N.
 21. The method according to claim 20wherein the compound is ##STR50##
 22. The method according to claim 1 or8 wherein the compound is 2-(t-butylsulfonyl)-2-propenyl chloroformate,benzothiophene sulfone-2-methyl chloroformate,2-(phenylsulfonyl)-2-propenyl chloroformate, 2-carboethoxy-2-propenylchloroformate, 2-(phenylsulfinyl)-2-propenyl chloroformate,(E)-3-phenyl-2-(phenylsulfonyl)-2-propenyl chloroformate,(Z)-3-phenyl-2-(phenylsulfonyl)-2-propenyl chloroformate,3,3-dimethyl-2-(phenylsulfonyl)-2-propenyl chloroformate or3,3-diphenyl-2-(phenylsulfonyl)-2-propenyl chloroformate.
 23. The methodof claim 8 wherein the protecting group is removed by treating theproduct of (b) with a nucleophile.
 24. The method of claim 23 whereinthe nucleophile is a simple amine or an organomercaptan.
 25. The methodof claim 24 wherein the simple amine is HNR₅ R₆, wherein R₅ and R₆ areindependently hydrogen, lower alkyl or substituted lower alkyl, thelower alkyl being substituted with OH, CH₃ or CH₂ CH₃ and R₅ or R₆ takentogether form a ring containing 4 to 10 ring carbon atoms and up to tworing heteroatoms, wherein the heteroatoms are O, S or N.
 26. The methodof claim 25 wherein the nucleophile is piperidine,2,6-dimethylpiperidine, piperazine, morpholine, diethylamine,ethylamine, ethanolamine or benzylmercaptan.
 27. The method of claim 24wherein the simple amine is piperidine.
 28. The method of claim 23wherein the nucleophile is attached to a solid support.
 29. The methodaccording to claim 8 wherein the first and second amino acids are alphaamino acids.
 30. In the synthesis of peptides wherein a first N-α-aminoprotected amino acid is covalently coupled to a solid phase peptidesynthesis resin, the N-α-amino protecting group is cleaved off and theresulting free amino group is coupled via peptide linkage to thecarboxyl group of a second N-α-amino protected amino acid and the cyclerepeated until the desired peptide sequence has been obtained and thensaid peptide is cleaved from said resin,the improvement comprising usinga nucleophile labile N-α-amino protecting group on each of said aminoacids and using a nucleophile to cleave said protecting group in eachcycle, said N-α-amino protecting group being a 2-propenyloxycarbonyl ofthe formula: ##STR51## wherein R is an electron withdrawing group;X₁ andX₂ are independently H, lower alkyl, aryl, aryl lower-alkyl orpolystyrene or R and X₁ taken together with the carbon atoms to whichthey are attached form a monocyclic, bicyclic or tricylic ring so thatsaid compound has the formula: ##STR52## B is a chemical bond, CR₈ R₉,##STR53## SO₂, SO, or S, F is a chemical bond CR₁₂ R₁₃, SO₂, S, SO or##STR54## Ring G is absent or is a mono or bicyclic fused ringcontaining 5 to 10 ring carbon atoms and up to 2 ring heteroatoms,wherein said ring heteroatoms are S, N or O, with the proviso that whenring G is absent or does not contain a ring heteroatom, then at leastone of B or F is ##STR55## SO₂, SO or S; and R₈, R₉, R₁₁, R₁₂ and R₁₃are independently hydrogen or lower alkyl.
 31. The improved synthesisaccording to claim 30 wherein the nucleophile cleaves the protectinggroup by Michael-type addition to the double bond of the2-propenyloxycarbonyl.
 32. In the synthesis of peptides wherein a freeamino group of a first amino acid is coupled with an N-α-amino protectedamino acid through a peptide linkage to the carboxyl group of saidN-α-amino protected amino acid and the cycle is repeated until thedesired peptide sequence has been obtained, the improvement comprisingusing a nucleophile-labile N-α-amino protecting group on each amino acidand using a nucleophile to cleave said protecting group in each cycle,said N-α-amino protecting group being a 2-propenyloxycarbonyl of theformula: ##STR56## wherein R is an electron withdrawing group;X₁ and X₂are independently H, lower alkyl, aryl, aryl lower-alkyl or polystyreneor R and X₁ taken together with the carbon atoms to which they areattached form a monocyclic, bicyclic or tricylic ring so that saidcompound has the formula: ##STR57## B is a chemical bond, CR₈ R₉,##STR58## SO₂, SO or S, F is a chemical bond, CR₁₂ R₁₃ SO₂, S, SO or##STR59## Ring G is absent or is a mono- or bicyclic fused ringcontaining 5 to 10 ring carbon atoms and up to 2 ring heteroatoms,wherein said ring heteroatoms are S, N or O, with the proviso that whenRing G is absent or does not contain a ring heteroatom, then at leastone of B or F is ##STR60## SO₂, SO or S; and R₈, R₉, R₁₁, R₁₂ and R₁₃are independently hydrogen or lower alkyl.
 33. The improved synthesis ofclaim 30 or 32 wherein said nucleophile is an organic amine ororganomercaptan.
 34. The improved synthesis of claim 33 wherein theamine has the formula HNR₅ R₆, wherein R₅ and R₆ are independentlyhydrogen, lower alkyl or monosubstituted lower alkyl wherein thesubstituents are OH, or lower alkyl or R₅ and R₆ taken together form acycloalkyl or bicyclicalkyl containing from 4 to 10 ring carbon atoms ora heterocyclic ring containing 1 or 2 heteroatoms selected from thegroup consisting of nitrogen, sulfur, and oxygen, said heterocyclehaving 3-9 ring carbon atoms.
 35. The improved synthesis according toclaim 30 or 32 wherein X₂ is hydrogen, phenyl or lower alkyl having from1 to 4 carbon atoms.
 36. The improved synthesis according to claim 30 or32 wherein X₁ and X₂ are independently hydrogen, phenyl or lower alkylhaving from 1 to 4 carbon atoms.
 37. The improved synthesis according toclaim 30 or 32 wherein R is SO₂, SOR₂, COOR₂, COR₂, CHO, CONR₂ R₃, CN,CF₃, NO₂, aryl or pyridyl, and R₂ and R₃ are independently lower alkyl,aryl, aryl lower alkyl or heteroaryl.
 38. The improved synthesisaccording to claim 37 wherein R is SO₂ R₂, SOR₂, COOR₂, COR₂ CONR₂ R₃,aryl, 2-pyridyl or 4-pyridyl.
 39. The improved synthesis according claim38 wherein R is SO₂ C(CH₃)₃, SOC(CH₃)₃, SO₂ C₆ H₅, SOC₆ H₅, 2-pyridyl or4-pyridyl.
 40. The improved synthesis according to claim 30 or 32wherein R and X₁ taken together with the carbon atoms to which they areattached form the bicyclic or tricyclic ring.
 41. The improved synthesisaccording to claim 30 or 32 wherein the protecting group has theformula: ##STR61##
 42. The improved synthesis according to claim 41wherein the protecting group is ##STR62## wherein B is CR₈ R₉ or SO₂ ;Eand D are independently CH or N; R₈ and R₉ are independently hydrogen onlower alkyl; provided that when B is CR₈ R₉, then E or D is N.
 43. Theimproved synthesis according to claim 42, wherein the protecting groupis: ##STR63##
 44. The improved synthesis according to claim 30 or 32wherein the protecting group is 2-(t-butylsulfonyl)-2-propenyloxycarbonyl or benzothiophene sulfone-2-methyloxy carbonyl.
 45. Theimproved synthesis according to claim 32 wherein the nucleophile cleavessaid protecting group by Michael-type addition to the double bond of the2-propenyloxycarbonyl.
 46. The improved synthesis according to claim 33wherein the nucleophile is ethanolamine, morpholine, piperidine,diethylamine, 2,6-dimethylpiperidine, piperazine, dimethylamine,ethylamine or benzylmercaptan.